T

his file documents the GNU C library.

This is Edition 0.08 DRAFT, last updated 11 Jan 1999, of The GNU C Library Reference Manual, for Version 2.1 Beta.

Copyright (C) 1993, '94, '95, '96, '97, '98, '99 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU Library General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the text of the translation of the section entitled "GNU Library General Public License" must be approved for accuracy by the Foundation.

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This is Edition 0.08 DRAFT, last updated 11 Jan 1999, of The GNU C Library Reference Manual, for Version 2.1 Beta of the GNU C Library.

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Introduction

The C language provides no built-in facilities for performing such common operations as input/output, memory management, string manipulation, and the like. Instead, these facilities are defined in a standard library, which you compile and link with your programs.

The GNU C library, described in this document, defines all of the library functions that are specified by the ISO C standard, as well as additional features specific to POSIX and other derivatives of the Unix operating system, and extensions specific to the GNU system.

The purpose of this manual is to tell you how to use the facilities of the GNU library. We have mentioned which features belong to which standards to help you identify things that are potentially non-portable to other systems. But the emphasis in this manual is not on strict portability.

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Getting Started

This manual is written with the assumption that you are at least somewhat familiar with the C programming language and basic programming concepts. Specifically, familiarity with ISO standard C (see ISO C), rather than "traditional" pre-ISO C dialects, is assumed.

The GNU C library includes several header files, each of which provides definitions and declarations for a group of related facilities; this information is used by the C compiler when processing your program. For example, the header file stdio.h declares facilities for performing input and output, and the header file string.h declares string processing utilities. The organization of this manual generally follows the same division as the header files.

If you are reading this manual for the first time, you should read all of the introductory material and skim the remaining chapters. There are a lot of functions in the GNU C library and it's not realistic to expect that you will be able to remember exactly how to use each and every one of them. It's more important to become generally familiar with the kinds of facilities that the library provides, so that when you are writing your programs you can recognize when to make use of library functions, and where in this manual you can find more specific information about them.

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Standards and Portability

This section discusses the various standards and other sources that the GNU C library is based upon. These sources include the ISO C and POSIX standards, and the System V and Berkeley Unix implementations.

The primary focus of this manual is to tell you how to make effective use of the GNU library facilities. But if you are concerned about making your programs compatible with these standards, or portable to operating systems other than GNU, this can affect how you use the library. This section gives you an overview of these standards, so that you will know what they are when they are mentioned in other parts of the manual.

See Library Summary, for an alphabetical list of the functions and other symbols provided by the library. This list also states which standards each function or symbol comes from.

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ISO C

The GNU C library is compatible with the C standard adopted by the American National Standards Institute (ANSI): American National Standard X3.159-1989--"ANSI C" and later by the International Standardization Organization (ISO): ISO/IEC 9899:1990, "Programming languages--C". We here refer to the standard as ISO C since this is the more general standard in respect of ratification. The header files and library facilities that make up the GNU library are a superset of those specified by the ISO C standard.

If you are concerned about strict adherence to the ISO C standard, you should use the -ansi option when you compile your programs with the GNU C compiler. This tells the compiler to define only ISO standard features from the library header files, unless you explicitly ask for additional features. See Feature Test Macros, for information on how to do this.

Being able to restrict the library to include only ISO C features is important because ISO C puts limitations on what names can be defined by the library implementation, and the GNU extensions don't fit these limitations. See Reserved Names, for more information about these restrictions.

This manual does not attempt to give you complete details on the differences between ISO C and older dialects. It gives advice on how to write programs to work portably under multiple C dialects, but does not aim for completeness.

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POSIX (The Portable Operating System Interface)

The GNU library is also compatible with the ISO POSIX family of standards, known more formally as the Portable Operating System Interface for Computer Environments (ISO/IEC 9945). They were also published as ANSI/IEEE Std 1003. POSIX is derived mostly from various versions of the Unix operating system.

The library facilities specified by the POSIX standards are a superset of those required by ISO C; POSIX specifies additional features for ISO C functions, as well as specifying new additional functions. In general, the additional requirements and functionality defined by the POSIX standards are aimed at providing lower-level support for a particular kind of operating system environment, rather than general programming language support which can run in many diverse operating system environments.

The GNU C library implements all of the functions specified in ISO/IEC 9945-1:1996, the POSIX System Application Program Interface, commonly referred to as POSIX.1. The primary extensions to the ISO C facilities specified by this standard include file system interface primitives (see File System Interface), device-specific terminal control functions (see Low-Level Terminal Interface), and process control functions (see Processes).

Some facilities from ISO/IEC 9945-2:1993, the POSIX Shell and Utilities standard (POSIX.2) are also implemented in the GNU library. These include utilities for dealing with regular expressions and other pattern matching facilities (see Pattern Matching).

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Berkeley Unix

The GNU C library defines facilities from some versions of Unix which are not formally standardized, specifically from the 4.2 BSD, 4.3 BSD, and 4.4 BSD Unix systems (also known as Berkeley Unix) and from SunOS (a popular 4.2 BSD derivative that includes some Unix System V functionality). These systems support most of the ISO C and POSIX facilities, and 4.4 BSD and newer releases of SunOS in fact support them all.

The BSD facilities include symbolic links (see Symbolic Links), the select function (see Waiting for I/O), the BSD signal functions (see BSD Signal Handling), and sockets (see Sockets).

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SVID (The System V Interface Description)

The System V Interface Description (SVID) is a document describing the AT&T Unix System V operating system. It is to some extent a superset of the POSIX standard (see POSIX).

The GNU C library defines most of the facilities required by the SVID that are not also required by the ISO C or POSIX standards, for compatibility with System V Unix and other Unix systems (such as SunOS) which include these facilities. However, many of the more obscure and less generally useful facilities required by the SVID are not included. (In fact, Unix System V itself does not provide them all.)

The supported facilities from System V include the methods for inter-process communication and shared memory, the hsearch and drand48 families of functions, fmtmsg and several of the mathematical functions.

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XPG (The X/Open Portability Guide)

The X/Open Portability Guide, published by the X/Open Company, Ltd., is a more general standard than POSIX. X/Open owns the Unix copyright and the XPG specifies the requirements for systems which are intended to be a Unix system.

The GNU C library complies to the X/Open Portability Guide, Issue 4.2, with all extensions common to XSI (X/Open System Interface) compliant systems and also all X/Open UNIX extensions.

The additions on top of POSIX are mainly derived from functionality available in System V and BSD systems. Some of the really bad mistakes in System V systems were corrected, though. Since fulfilling the XPG standard with the Unix extensions is a precondition for getting the Unix brand chances are good that the functionality is available on commercial systems.

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Using the Library

This section describes some of the practical issues involved in using the GNU C library.

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Header Files

Libraries for use by C programs really consist of two parts: header files that define types and macros and declare variables and functions; and the actual library or archive that contains the definitions of the variables and functions.

(Recall that in C, a declaration merely provides information that a function or variable exists and gives its type. For a function declaration, information about the types of its arguments might be provided as well. The purpose of declarations is to allow the compiler to correctly process references to the declared variables and functions. A definition, on the other hand, actually allocates storage for a variable or says what a function does.)

In order to use the facilities in the GNU C library, you should be sure that your program source files include the appropriate header files. This is so that the compiler has declarations of these facilities available and can correctly process references to them. Once your program has been compiled, the linker resolves these references to the actual definitions provided in the archive file.

Header files are included into a program source file by the #include preprocessor directive. The C language supports two forms of this directive; the first, 

#include "header"

is typically used to include a header file header that you write yourself; this would contain definitions and declarations describing the interfaces between the different parts of your particular application. By contrast, 

#include <file.h>

is typically used to include a header file file.h that contains definitions and declarations for a standard library. This file would normally be installed in a standard place by your system administrator. You should use this second form for the C library header files.

Typically, #include directives are placed at the top of the C source file, before any other code. If you begin your source files with some comments explaining what the code in the file does (a good idea), put the #include directives immediately afterwards, following the feature test macro definition (see Feature Test Macros).

For more information about the use of header files and #include directives, see Header Files.

The GNU C library provides several header files, each of which contains the type and macro definitions and variable and function declarations for a group of related facilities. This means that your programs may need to include several header files, depending on exactly which facilities you are using.

Some library header files include other library header files automatically. However, as a matter of programming style, you should not rely on this; it is better to explicitly include all the header files required for the library facilities you are using. The GNU C library header files have been written in such a way that it doesn't matter if a header file is accidentally included more than once; including a header file a second time has no effect. Likewise, if your program needs to include multiple header files, the order in which they are included doesn't matter.

Compatibility Note: Inclusion of standard header files in any order and any number of times works in any ISO C implementation. However, this has traditionally not been the case in many older C implementations.

Strictly speaking, you don't have to include a header file to use a function it declares; you could declare the function explicitly yourself, according to the specifications in this manual. But it is usually better to include the header file because it may define types and macros that are not otherwise available and because it may define more efficient macro replacements for some functions. It is also a sure way to have the correct declaration.

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Macro Definitions of Functions

If we describe something as a function in this manual, it may have a macro definition as well. This normally has no effect on how your program runs--the macro definition does the same thing as the function would. In particular, macro equivalents for library functions evaluate arguments exactly once, in the same way that a function call would. The main reason for these macro definitions is that sometimes they can produce an inline expansion that is considerably faster than an actual function call.

Taking the address of a library function works even if it is also defined as a macro. This is because, in this context, the name of the function isn't followed by the left parenthesis that is syntactically necessary to recognize a macro call.

You might occasionally want to avoid using the macro definition of a function--perhaps to make your program easier to debug. There are two ways you can do this:

For example, suppose the header file stdlib.h declares a function named abs with 

extern int abs (int);

and also provides a macro definition for abs. Then, in: 

#include <stdlib.h>
int f (int *i) { return abs (++*i); }

the reference to abs might refer to either a macro or a function. On the other hand, in each of the following examples the reference is to a function and not a macro. 

#include <stdlib.h>
int g (int *i) { return (abs) (++*i); }

#undef abs
int h (int *i) { return abs (++*i); }

Since macro definitions that double for a function behave in exactly the same way as the actual function version, there is usually no need for any of these methods. In fact, removing macro definitions usually just makes your program slower.

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Reserved Names

The names of all library types, macros, variables and functions that come from the ISO C standard are reserved unconditionally; your program may not redefine these names. All other library names are reserved if your program explicitly includes the header file that defines or declares them. There are several reasons for these restrictions:

In addition to the names documented in this manual, reserved names include all external identifiers (global functions and variables) that begin with an underscore (_) and all identifiers regardless of use that begin with either two underscores or an underscore followed by a capital letter are reserved names. This is so that the library and header files can define functions, variables, and macros for internal purposes without risk of conflict with names in user programs.

Some additional classes of identifier names are reserved for future extensions to the C language or the POSIX.1 environment. While using these names for your own purposes right now might not cause a problem, they do raise the possibility of conflict with future versions of the C or POSIX standards, so you should avoid these names.

In addition, some individual header files reserve names beyond those that they actually define. You only need to worry about these restrictions if your program includes that particular header file.

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Feature Test Macros

The exact set of features available when you compile a source file is controlled by which feature test macros you define.

If you compile your programs using gcc -ansi, you get only the ISO C library features, unless you explicitly request additional features by defining one or more of the feature macros. See Invoking GCC, for more information about GCC options.

You should define these macros by using #define preprocessor directives at the top of your source code files. These directives must come before any #include of a system header file. It is best to make them the very first thing in the file, preceded only by comments. You could also use the -D option to GCC, but it's better if you make the source files indicate their own meaning in a self-contained way.

This system exists to allow the library to conform to multiple standards. Although the different standards are often described as supersets of each other, they are usually incompatible because larger standards require functions with names that smaller ones reserve to the user program. This is not mere pedantry -- it has been a problem in practice. For instance, some non-GNU programs define functions named getline that have nothing to do with this library's getline. They would not be compilable if all features were enabled indiscriminately.

This should not be used to verify that a program conforms to a limited standard. It is insufficient for this purpose, as it will not protect you from including header files outside the standard, or relying on semantics undefined within the standard.

_POSIX_SOURCE Macro
If you define this macro, then the functionality from the POSIX.1 standard (IEEE Standard 1003.1) is available, as well as all of the ISO C facilities.

The state of _POSIX_SOURCE is irrelevant if you define the macro _POSIX_C_SOURCE to a positive integer.

_POSIX_C_SOURCE Macro
Define this macro to a positive integer to control which POSIX functionality is made available. The greater the value of this macro, the more functionality is made available.

If you define this macro to a value greater than or equal to 1, then the functionality from the 1990 edition of the POSIX.1 standard (IEEE Standard 1003.1-1990) is made available.

If you define this macro to a value greater than or equal to 2, then the functionality from the 1992 edition of the POSIX.2 standard (IEEE Standard 1003.2-1992) is made available.

If you define this macro to a value greater than or equal to 199309L, then the functionality from the 1993 edition of the POSIX.1b standard (IEEE Standard 1003.1b-1993) is made available.

Greater values for _POSIX_C_SOURCE will enable future extensions. The POSIX standards process will define these values as necessary, and the GNU C Library should support them some time after they become standardized. The 1996 edition of POSIX.1 (ISO/IEC 9945-1: 1996) states that if you define _POSIX_C_SOURCE to a value greater than or equal to 199506L, then the functionality from the 1996 edition is made available.

The Single Unix Specification specify that setting this macro to the value 199506L selects all the values specified by the POSIX standards plus those of the Single Unix Specification, i.e., is the same as if _XOPEN_SOURCE is set to 500 (see below).

_BSD_SOURCE Macro
If you define this macro, functionality derived from 4.3 BSD Unix is included as well as the ISO C, POSIX.1, and POSIX.2 material.

Some of the features derived from 4.3 BSD Unix conflict with the corresponding features specified by the POSIX.1 standard. If this macro is defined, the 4.3 BSD definitions take precedence over the POSIX definitions.

Due to the nature of some of the conflicts between 4.3 BSD and POSIX.1, you need to use a special BSD compatibility library when linking programs compiled for BSD compatibility. This is because some functions must be defined in two different ways, one of them in the normal C library, and one of them in the compatibility library. If your program defines _BSD_SOURCE, you must give the option -lbsd-compat to the compiler or linker when linking the program, to tell it to find functions in this special compatibility library before looking for them in the normal C library.

_SVID_SOURCE Macro
If you define this macro, functionality derived from SVID is included as well as the ISO C, POSIX.1, POSIX.2, and X/Open material.

_XOPEN_SOURCE Macro
_XOPEN_SOURCE_EXTENDED Macro
If you define this macro, functionality described in the X/Open Portability Guide is included. This is a superset of the POSIX.1 and POSIX.2 functionality and in fact _POSIX_SOURCE and _POSIX_C_SOURCE are automatically defined.

As the unification of all Unices, functionality only available in BSD and SVID is also included.

If the macro _XOPEN_SOURCE_EXTENDED is also defined, even more functionality is available. The extra functions will make all functions available which are necessary for the X/Open Unix brand.

If the macro _XOPEN_SOURCE has the value 500 this includes all functionality described so far plus some new definitions from the Single Unix Specification, version 2.

_LARGEFILE_SOURCE Macro
If this macro is defined some extra functions are available which rectify a few shortcomings in all previous standards. More concrete the functions fseeko and ftello are available. Without these functions the difference between the ISO C interface (fseek, ftell) and the low-level POSIX interface (lseek) would lead to problems.

This macro was introduced as part of the Large File Support extension (LFS).

_LARGEFILE64_SOURCE Macro
If you define this macro an additional set of function gets available which enables to use on 32 bit systems to use files of sizes beyond the usual limit of 2GB. This interface is not available if the system does not support files that large. On systems where the natural file size limit is greater than 2GB (i.e., on 64 bit systems) the new functions are identical to the replaced functions.

The new functionality is made available by a new set of types and functions which replace existing. The names of these new objects contain 64 to indicate the intention, e.g., off_t vs. off64_t and fseeko vs. fseeko64.

This macro was introduced as part of the Large File Support extension (LFS). It is a transition interface for the time 64 bit offsets are not generally used (see _FILE_OFFSET_BITS.

_FILE_OFFSET_BITS Macro
This macro lets decide which file system interface shall be used, one replacing the other. While _LARGEFILE64_SOURCE makes the 64 bit interface available as an additional interface _FILE_OFFSET_BITS allows to use the 64 bit interface to replace the old interface.

If _FILE_OFFSET_BITS is undefined or if it is defined to the value 32 nothing changes. The 32 bit interface is used and types like off_t have a size of 32 bits on 32 bit systems.

If the macro is defined to the value 64 the large file interface replaces the old interface. I.e., the functions are not made available under different names as _LARGEFILE64_SOURCE does. Instead the old function names now reference the new functions, e.g., a call to fseeko now indeed calls fseeko64.

This macro should only be selected if the system provides mechanisms for handling large files. On 64 bit systems this macro has no effect since the *64 functions are identical to the normal functions.

This macro was introduced as part of the Large File Support extension (LFS).

_GNU_SOURCE Macro
If you define this macro, everything is included: ISO C, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU extensions. In the cases where POSIX.1 conflicts with BSD, the POSIX definitions take precedence.

If you want to get the full effect of _GNU_SOURCE but make the BSD definitions take precedence over the POSIX definitions, use this sequence of definitions: 

#define _GNU_SOURCE
#define _BSD_SOURCE
#define _SVID_SOURCE

Note that if you do this, you must link your program with the BSD compatibility library by passing the -lbsd-compat option to the compiler or linker. Note: If you forget to do this, you may get very strange errors at run time.

_REENTRANT Macro
_THREAD_SAFE Macro
If you define one of these macros, reentrant versions of several functions get declared. Some of the functions are specified in POSIX.1c but many others are only available on a few other systems or are unique to GNU libc. The problem is that the standardization of the thread safe C library interface still is behind.

Unlike on some other systems no special version of the C library must be used for linking. There is only one version but while compiling this it must have been specified to compile as thread safe.

We recommend you use _GNU_SOURCE in new programs. If you don't specify the -ansi option to GCC and don't define any of these macros explicitly, the effect is the same as defining _POSIX_C_SOURCE to 2 and _POSIX_SOURCE, _SVID_SOURCE, and _BSD_SOURCE to 1.

When you define a feature test macro to request a larger class of features, it is harmless to define in addition a feature test macro for a subset of those features. For example, if you define _POSIX_C_SOURCE, then defining _POSIX_SOURCE as well has no effect. Likewise, if you define _GNU_SOURCE, then defining either _POSIX_SOURCE or _POSIX_C_SOURCE or _SVID_SOURCE as well has no effect.

Note, however, that the features of _BSD_SOURCE are not a subset of any of the other feature test macros supported. This is because it defines BSD features that take precedence over the POSIX features that are requested by the other macros. For this reason, defining _BSD_SOURCE in addition to the other feature test macros does have an effect: it causes the BSD features to take priority over the conflicting POSIX features.

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Roadmap to the Manual

Here is an overview of the contents of the remaining chapters of this manual.

If you already know the name of the facility you are interested in, you can look it up in Library Summary. This gives you a summary of its syntax and a pointer to where you can find a more detailed description. This appendix is particularly useful if you just want to verify the order and type of arguments to a function, for example. It also tells you what standard or system each function, variable, or macro is derived from.

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Error Reporting

Many functions in the GNU C library detect and report error conditions, and sometimes your programs need to check for these error conditions. For example, when you open an input file, you should verify that the file was actually opened correctly, and print an error message or take other appropriate action if the call to the library function failed.

This chapter describes how the error reporting facility works. Your program should include the header file errno.h to use this facility.

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Checking for Errors

Most library functions return a special value to indicate that they have failed. The special value is typically -1, a null pointer, or a constant such as EOF that is defined for that purpose. But this return value tells you only that an error has occurred. To find out what kind of error it was, you need to look at the error code stored in the variable errno. This variable is declared in the header file errno.h.

volatile int errno Variable
The variable errno contains the system error number. You can change the value of errno.

Since errno is declared volatile, it might be changed asynchronously by a signal handler; see Defining Handlers. However, a properly written signal handler saves and restores the value of errno, so you generally do not need to worry about this possibility except when writing signal handlers.

The initial value of errno at program startup is zero. Many library functions are guaranteed to set it to certain nonzero values when they encounter certain kinds of errors. These error conditions are listed for each function. These functions do not change errno when they succeed; thus, the value of errno after a successful call is not necessarily zero, and you should not use errno to determine whether a call failed. The proper way to do that is documented for each function. If the call the failed, you can examine errno.

Many library functions can set errno to a nonzero value as a result of calling other library functions which might fail. You should assume that any library function might alter errno when the function returns an error.

Portability Note: ISO C specifies errno as a "modifiable lvalue" rather than as a variable, permitting it to be implemented as a macro. For example, its expansion might involve a function call, like *_errno (). In fact, that is what it is on the GNU system itself. The GNU library, on non-GNU systems, does whatever is right for the particular system.

There are a few library functions, like sqrt and atan, that return a perfectly legitimate value in case of an error, but also set errno. For these functions, if you want to check to see whether an error occurred, the recommended method is to set errno to zero before calling the function, and then check its value afterward.

All the error codes have symbolic names; they are macros defined in errno.h. The names start with E and an upper-case letter or digit; you should consider names of this form to be reserved names. See Reserved Names.

The error code values are all positive integers and are all distinct, with one exception: EWOULDBLOCK and EAGAIN are the same. Since the values are distinct, you can use them as labels in a switch statement; just don't use both EWOULDBLOCK and EAGAIN. Your program should not make any other assumptions about the specific values of these symbolic constants.

The value of errno doesn't necessarily have to correspond to any of these macros, since some library functions might return other error codes of their own for other situations. The only values that are guaranteed to be meaningful for a particular library function are the ones that this manual lists for that function.

On non-GNU systems, almost any system call can return EFAULT if it is given an invalid pointer as an argument. Since this could only happen as a result of a bug in your program, and since it will not happen on the GNU system, we have saved space by not mentioning EFAULT in the descriptions of individual functions.

In some Unix systems, many system calls can also return EFAULT if given as an argument a pointer into the stack, and the kernel for some obscure reason fails in its attempt to extend the stack. If this ever happens, you should probably try using statically or dynamically allocated memory instead of stack memory on that system.

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Error Codes

The error code macros are defined in the header file errno.h. All of them expand into integer constant values. Some of these error codes can't occur on the GNU system, but they can occur using the GNU library on other systems.

int EPERM Macro
Operation not permitted; only the owner of the file (or other resource) or processes with special privileges can perform the operation.

int ENOENT Macro
No such file or directory. This is a "file doesn't exist" error for ordinary files that are referenced in contexts where they are expected to already exist.

int ESRCH Macro
No process matches the specified process ID.

int EINTR Macro
Interrupted function call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular operation;on call; an asynchronous signal occurred and prevented completion of the call. When this happens, you should try the call again.

You can choose to have functions resume after a signal that is handled, rather than failing with EINTR; see Interrupted Primitives.

int EIO Macro
Input/output error; usually used for physical read or write errors.

int ENXIO Macro
No such device or address. The system tried to use the device represented by a file you specified, and it couldn't find the device. This can mean that the device file was installed incorrectly, or that the physical device is missing or not correctly attached to the computer.

int E2BIG Macro
Argument list too long; used when the arguments passed to a new program being executed with one of the exec functions (see Executing a File) occupy too much memory space. This condition never arises in the GNU system.

int ENOEXEC Macro
Invalid executable file format. This condition is detected by the exec functions; see Executing a File.

int EBADF Macro
Bad file descriptor; for example, I/O on a descriptor that has been closed or reading from a descriptor open only for writing (or vice versa).

int ECHILD Macro
There are no child processes. This error happens on operations that are supposed to manipulate child processes, when there aren't any processes to manipulate.

int EDEADLK Macro
Deadlock avoided; allocating a system resource would have resulted in a deadlock situation. The system does not guarantee that it will notice all such situations. This error means you got lucky and the system noticed; it might just hang. See File Locks, for an example.

int ENOMEM Macro
No memory available. The system cannot allocate more virtual memory because its capacity is full.

int EACCES Macro
Permission denied; the file permissions do not allow the attempted operation.

int EFAULT Macro
Bad address; an invalid pointer was detected. In the GNU system, this error never happens; you get a signal instead.

int ENOTBLK Macro
A file that isn't a block special file was given in a situation that requires one. For example, trying to mount an ordinary file as a file system in Unix gives this error.

int EBUSY Macro
Resource busy; a system resource that can't be shared is already in use. For example, if you try to delete a file that is the root of a currently mounted filesystem, you get this error.

int EEXIST Macro
File exists; an existing file was specified in a context where it only makes sense to specify a new file.

int EXDEV Macro
An attempt to make an improper link across file systems was detected. This happens not only when you use link (see Hard Links) but also when you rename a file with rename (see Renaming Files).

int ENODEV Macro
The wrong type of device was given to a function that expects a particular sort of device.

int ENOTDIR Macro
A file that isn't a directory was specified when a directory is required.

int EISDIR Macro
File is a directory; you cannot open a directory for writing, or create or remove hard links to it.

int EINVAL Macro
Invalid argument. This is used to indicate various kinds of problems with passing the wrong argument to a library function.

int EMFILE Macro
The current process has too many files open and can't open any more. Duplicate descriptors do count toward this limit.

In BSD and GNU, the number of open files is controlled by a resource limit that can usually be increased. If you get this error, you might want to increase the RLIMIT_NOFILE limit or make it unlimited; see Limits on Resources.

int ENFILE Macro
There are too many distinct file openings in the entire system. Note that any number of linked channels count as just one file opening; see Linked Channels. This error never occurs in the GNU system.

int ENOTTY Macro
Inappropriate I/O control operation, such as trying to set terminal modes on an ordinary file.

int ETXTBSY Macro
An attempt to execute a file that is currently open for writing, or write to a file that is currently being executed. Often using a debugger to run a program is considered having it open for writing and will cause this error. (The name stands for "text file busy".) This is not an error in the GNU system; the text is copied as necessary.

int EFBIG Macro
File too big; the size of a file would be larger than allowed by the system.

int ENOSPC Macro
No space left on device; write operation on a file failed because the disk is full.

int ESPIPE Macro
Invalid seek operation (such as on a pipe).

int EROFS Macro
An attempt was made to modify something on a read-only file system.

int EMLINK Macro
Too many links; the link count of a single file would become too large. rename can cause this error if the file being renamed already has as many links as it can take (see Renaming Files).

int EPIPE Macro
Broken pipe; there is no process reading from the other end of a pipe. Every library function that returns this error code also generates a SIGPIPE signal; this signal terminates the program if not handled or blocked. Thus, your program will never actually see EPIPE unless it has handled or blocked SIGPIPE.

int EDOM Macro
Domain error; used by mathematical functions when an argument value does not fall into the domain over which the function is defined.

int ERANGE Macro
Range error; used by mathematical functions when the result value is not representable because of overflow or underflow.

int EAGAIN Macro
Resource temporarily unavailable; the call might work if you try again later. The macro EWOULDBLOCK is another name for EAGAIN; they are always the same in the GNU C library.

This error can happen in a few different situations:

  • An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation). You can use select to find out when the operation will be possible; see Waiting for I/O.

    Portability Note: In many older Unix systems, this condition was indicated by EWOULDBLOCK, which was a distinct error code different from EAGAIN. To make your program portable, you should check for both codes and treat them the same.

  • A temporary resource shortage made an operation impossible. fork can return this error. It indicates that the shortage is expected to pass, so your program can try the call again later and it may succeed. It is probably a good idea to delay for a few seconds before trying it again, to allow time for other processes to release scarce resources. Such shortages are usually fairly serious and affect the whole system, so usually an interactive program should report the error to the user and return to its command loop.

int EWOULDBLOCK Macro
In the GNU C library, this is another name for EAGAIN (above). The values are always the same, on every operating system.

C libraries in many older Unix systems have EWOULDBLOCK as a separate error code.

int EINPROGRESS Macro
An operation that cannot complete immediately was initiated on an object that has non-blocking mode selected. Some functions that must always block (such as connect; see Connecting) never return EAGAIN. Instead, they return EINPROGRESS to indicate that the operation has begun and will take some time. Attempts to manipulate the object before the call completes return EALREADY. You can use the select function to find out when the pending operation has completed; see Waiting for I/O.

int EALREADY Macro
An operation is already in progress on an object that has non-blocking mode selected.

int ENOTSOCK Macro
A file that isn't a socket was specified when a socket is required.

int EMSGSIZE Macro
The size of a message sent on a socket was larger than the supported maximum size.

int EPROTOTYPE Macro
The socket type does not support the requested communications protocol.

int ENOPROTOOPT Macro
You specified a socket option that doesn't make sense for the particular protocol being used by the socket. See Socket Options.

int EPROTONOSUPPORT Macro
The socket domain does not support the requested communications protocol (perhaps because the requested protocol is completely invalid). See Creating a Socket.

int ESOCKTNOSUPPORT Macro
The socket type is not supported.

int EOPNOTSUPP Macro
The operation you requested is not supported. Some socket functions don't make sense for all types of sockets, and others may not be implemented for all communications protocols. In the GNU system, this error can happen for many calls when the object does not support the particular