Configuration Files

Main Configuration Files

Related Modules	Related Directives
mod_mime	<IfDefine> Include TypesConfig

Apache is configured by placing directives in plain text configuration files. The main configuration file is usually called httpd.conf. The location of this file is set at compile-time, but may be overridden with the -f command line flag. In addition, other configuration files may be added using the Include directive, and wildcards can be used to include many configuration files. Any directive may be placed in any of these configuration files. Changes to the main configuration files are only recognized by Apache when it is started or restarted.

The server also reads a file containing mime document types; the filename is set by the TypesConfig directive, and is mime.types by default.

Syntax of the Configuration Files

Apache configuration files contain one directive per line. The back-slash "\" may be used as the last character on a line to indicate that the directive continues onto the next line. There must be no other characters or white space between the back-slash and the end of the line.

Directives in the configuration files are case-insensitive, but arguments to directives are often case sensitive. Lines that begin with the hash character "#" are considered comments, and are ignored. Comments may not be included on a line after a configuration directive. Blank lines and white space occurring before a directive are ignored, so you may indent directives for clarity.

You can check your configuration files for syntax errors without starting the server by using apache2ctl configtest or the -t command line option.

Modules

Related Modules	Related Directives
mod_so	<IfModule> LoadModule

Apache is a modular server. This implies that only the most basic functionality is included in the core server. Extended features are available through modules which can be loaded into Apache. By default, a base set of modules is included in the server at compile-time. If the server is compiled to use dynamically loaded modules, then modules can be compiled separately and added at any time using the LoadModule directive. Otherwise, Apache must be recompiled to add or remove modules. Configuration directives may be included conditional on a presence of a particular module by enclosing them in an <IfModule> block.

To see which modules are currently compiled into the server, you can use the -l command line option.

Scope of Directives

Related Modules	Related Directives
	<Directory> <DirectoryMatch> <Files> <FilesMatch> <Location> <LocationMatch> <VirtualHost>

Directives placed in the main configuration files apply to the entire server. If you wish to change the configuration for only a part of the server, you can scope your directives by placing them in <Directory>, <DirectoryMatch>, <Files>, <FilesMatch>, <Location>, and <LocationMatch> sections. These sections limit the application of the directives which they enclose to particular filesystem locations or URLs. They can also be nested, allowing for very fine grained configuration.

Apache has the capability to serve many different websites simultaneously. This is called Virtual Hosting. Directives can also be scoped by placing them inside <VirtualHost> sections, so that they will only apply to requests for a particular website.

Although most directives can be placed in any of these sections, some directives do not make sense in some contexts. For example, directives controlling process creation can only be placed in the main server context. To find which directives can be placed in which sections, check the Context of the directive. For further information, we provide details on ode class=module">mod_charset_lite, transcodes between different character sets.

mod_ext_filter, runs an external program as a filter.

Apache also uses a number of filters internally to perform functions like chunking and byte-range handling.

A wider range of applications are implemented by third-party filter modules available from modules.apache.org and elsewhere. A few of these are:

• HTML and XML processing and rewriting
• XSLT transforms and XIncludes
• XML Namespace support
• File Upload handling and decoding of HTML Forms
• Image processing
• Protection of vulnerable applications such as PHP scripts
• Text search-and-replace editing

Smart Filtering

mod_filter, included in Apache 2.1 and later, enables the filter chain to be configured dynamically at run time. So for example you can set up a proxy to rewrite HTML with an HTML filter and JPEG images with a completely separate filter, despite the proxy having no prior information about what the origin server will send. This works by using a filter harness, that dispatches to different providers according to the actual contents at runtime. Any filter may be either inserted directly in the chain and run unconditionally, or used as a provider and inserted dynamically. For example,

• an HTML processing filter will only run if the content is text/html or application/xhtml+xml
• A compression filter will only run if the input is a compressible type and not already compressed
• A charset conversion filter will be inserted if a text document is not already in the desired charset

Using Filters

There are two ways to use filtering: Simple and Dynamic. In general, you should use one or the other; mixing them can have unexpected consequences (although simple Input filtering can be mixed freely with either simple or dynamic Output filtering).

The Simple Way is the only way to configure input filters, and is sufficient for output filters where you need a static filter chain. Relevant directives are SetInputFilter,