Chapter 13. System and Administrative Commands
The startup and shutdown scripts in /etc/rc.d illustrate the uses (and usefulness) of many of these comands. These are usually invoked by root and used for system maintenance or emergency filesystem repairs. Use with caution, as some of these commands may damage your system if misused.
- users
Show all logged on users. This is the approximate equivalent of who -q.
- groups
Lists the current user and the groups she belongs to. This corresponds to the $GROUPS internal variable, but gives the group names, rather than the numbers.
bash$ groups bozita cdrom cdwriter audio xgrp bash$ echo $GROUPS 501
- chown, chgrp
The chown command changes the ownership of a file or files. This command is a useful method that root can use to shift file ownership from one user to another. An ordinary user may not change the ownership of files, not even her own files. [1]
root# chown bozo *.txt
The chgrp command changes the group ownership of a file or files. You must be owner of the file(s) as well as a member of the destination group (or root) to use this operation.
1 chgrp --recursive dunderheads *.data 2 # The "dunderheads" group will now own all the "*.data" files 3 #+ all the way down the $PWD directory tree (that's what "recursive" means).
- useradd, userdel
The useradd administrative command adds a user account to the system and creates a home directory for that particular user, if so specified. The corresponding userdel command removes a user account from the system [2] and deletes associated files.
The adduser command is a synonym for useradd and is usually a symbolic link to it.
- usermod
Modify a user account. Changes may be made to the password, group membership, expiration date, and other attributes of a given user's account. With this command, a user's password may be locked, which has the effect of disabling the account.
- groupmod
Modify a given group. The group name and/or ID number may be changed using this command.
- id
The id command lists the real and effective user IDs and the group IDs of the user associated with the current process. This is the counterpart to the $UID, $EUID, and $GROUPS internal Bash variables.
bash$ id uid=501(bozo) gid=501(bozo) groups=501(bozo),22(cdrom),80(cdwriter),81(audio) bash$ echo $UID 501
The id command shows the effective IDs only when they differ from the real ones.
Also see Example 9-5.
- who
Show all users logged on to the system.
bash$ who bozo tty1 Apr 27 17:45 bozo pts/0 Apr 27 17:46 bozo pts/1 Apr 27 17:47 bozo pts/2 Apr 27 17:49
The -m gives detailed information about only the current user. Passing any two arguments to who is the equivalent of who -m, as in who am i or who The Man.
bash$ who -m localhost.localdomain!bozo pts/2 Apr 27 17:49
whoami is similar to who -m, but only lists the user name.
bash$ whoami bozo
- w
Show all logged on users and the processes belonging to them. This is an extended version of who. The output of w may be piped to grep to find a specific user and/or process.
bash$ w | grep startx bozo tty1 - 4:22pm 6:41 4.47s 0.45s startx
- logname
Show current user's login name (as found in /var/run/utmp). This is a near-equivalent to whoami, above.
bash$ logname bozo bash$ whoami bozo
However...
bash$ su Password: ...... bash# whoami root bash# logname bozo
While logname prints the name of the logged in user, whoami gives the name of the user attached to the current process. As we have just seen, sometimes these are not the same.
- su
Runs a program or script as a substitute user. su rjones starts a shell as user rjones. A naked su defaults to root. See Example A-15.
- sudo
Runs a command as root (or another user). This may be used in a script, thus permitting a regular user to run the script.
1 #!/bin/bash 2 3 # Some commands. 4 sudo cp /root/secretfile /home/bozo/secret 5 # Some more commands.
The file /etc/sudoers holds the names of users permitted to invoke sudo.
- passwd
Sets, changes, or manages a user's password.
The passwd command can be used in a script, but should not be.
Example 13-1. Setting a new password
1 #!/bin/bash 2 # setnew-password.sh: For demonstration purposes only. 3 # Not a good idea to actually run this script. 4 # This script must be run as root. 5 6 ROOT_UID=0 # Root has $UID 0. 7 E_WRONG_USER=65 # Not root? 8 9 E_NOSUCHUSER=70 10 SUCCESS=0 11 12 13 if [ "$UID" -ne "$ROOT_UID" ] 14 then 15 echo; echo "Only root can run this script."; echo 16 exit $E_WRONG_USER 17 else 18 echo 19 echo "You should know better than to run this script, root." 20 echo "Even root users get the blues... " 21 echo 22 fi 23 24 25 username=bozo 26 NEWPASSWORD=security_violation 27 28 # Check if bozo lives here. 29 grep -q "$username" /etc/passwd 30 if [ $? -ne $SUCCESS ] 31 then 32 echo "User $username does not exist." 33 echo "No password changed." 34 exit $E_NOSUCHUSER 35 fi 36 37 echo "$NEWPASSWORD" | passwd --stdin "$username" 38 # The '--stdin' option to 'passwd' permits 39 #+ getting a new password from stdin (or a pipe). 40 41 echo; echo "User $username's password changed!" 42 43 # Using the 'passwd' command in a script is dangerous. 44 45 exit 0
The passwd command's -l, -u, and -d options permit locking, unlocking, and deleting a user's password. Only root may use these options.
- ac
Show users' logged in time, as read from /var/log/wtmp. This is one of the GNU accounting utilities.
bash$ ac total 68.08- last
List last logged in users, as read from /var/log/wtmp. This command can also show remote logins.
For example, to show the last few times the system rebooted:
bash$ last reboot reboot system boot 2.6.9-1.667 Fri Feb 4 18:18 (00:02) reboot system boot 2.6.9-1.667 Fri Feb 4 15:20 (01:27) reboot system boot 2.6.9-1.667 Fri Feb 4 12:56 (00:49) reboot system boot 2.6.9-1.667 Thu Feb 3 21:08 (02:17) . . . wtmp begins Tue Feb 1 12:50:09 2005
- newgrp
Change user's group ID without logging out. This permits access to the new group's files. Since users may be members of multiple groups simultaneously, this command finds little use.
- tty
Echoes the name of the current user's terminal. Note that each separate xterm window counts as a different terminal.
bash$ tty /dev/pts/1
- stty
Shows and/or changes terminal settings. This complex command, used in a script, can control terminal behavior and the way output displays. See the info page, and study it carefully.
Example 13-2. Setting an erase character
1 #!/bin/bash 2 # erase.sh: Using "stty" to set an erase character when reading input. 3 4 echo -n "What is your name? " 5 read name # Try to backspace 6 #+ to erase characters of input. 7 # Problems? 8 echo "Your name is $name." 9 10 stty erase '#' # Set "hashmark" (#) as erase character. 11 echo -n "What is your name? " 12 read name # Use # to erase last character typed. 13 echo "Your name is $name." 14 15 # Warning: Even after the script exits, the new key value remains set. 16 17 exit 0
Example 13-3. secret password: Turning off terminal echoing
1 #!/bin/bash 2 3 echo 4 echo -n "Enter password " 5 read passwd 6 echo "password is $passwd" 7 echo -n "If someone had been looking over your shoulder, " 8 echo "your password would have been compromised." 9 10 echo && echo # Two line-feeds in an "and list". 11 12 stty -echo # Turns off screen echo. 13 14 echo -n "Enter password again " 15 read passwd 16 echo 17 echo "password is $passwd" 18 echo 19 20 stty echo # Restores screen echo. 21 22 exit 0
A creative use of stty is detecting a user keypress (without hitting ENTER).
Example 13-4. Keypress detection
1 #!/bin/bash 2 # keypress.sh: Detect a user keypress ("hot keyboard"). 3 4 echo 5 6 old_tty_settings=$(stty -g) # Save old settings. 7 stty -icanon 8 Keypress=$(head -c1) # or $(dd bs=1 count=1 2> /dev/null) 9 # on non-GNU systems 10 11 echo 12 echo "Key pressed was \""$Keypress"\"." 13 echo 14 15 stty "$old_tty_settings" # Restore old settings. 16 17 # Thanks, Stephane Chazelas. 18 19 exit 0Also see Example 9-3.
- setterm
Set certain terminal attributes. This command writes to its terminal's stdout a string that changes the behavior of that terminal.
bash$ setterm -cursor off bash$
The setterm command can be used within a script to change the appearance of text written to stdout, although there are certainly better tools available for this purpose.
1 setterm -bold on 2 echo bold hello 3 4 setterm -bold off 5 echo normal hello
- tset
Show or initialize terminal settings. This is a less capable version of stty.
bash$ tset -r Terminal type is xterm-xfree86. Kill is control-U (^U). Interrupt is control-C (^C).
- setserial
Set or display serial port parameters. This command must be run by root user and is usually found in a system setup script.
1 # From /etc/pcmcia/serial script: 2 3 IRQ=`setserial /dev/$DEVICE | sed -e 's/.*IRQ: //'` 4 setserial /dev/$DEVICE irq 0 ; setserial /dev/$DEVICE irq $IRQ
- getty, agetty
The initialization process for a terminal uses getty or agetty to set it up for login by a user. These commands are not used within user shell scripts. Their scripting counterpart is stty.
- mesg
Enables or disables write access to the current user's terminal. Disabling access would prevent another user on the network to write to the terminal.
It can be very annoying to have a message about ordering pizza suddenly appear in the middle of the text file you are editing. On a multi-user network, you might therefore wish to disable write access to your terminal when you need to avoid interruptions.
- wall
This is an acronym for "write all", i.e., sending a message to all users at every terminal logged into the network. It is primarily a system administrator's tool, useful, for example, when warning everyone that the system will shortly go down due to a problem (see Example 17-2).
bash$ wall System going down for maintenance in 5 minutes! Broadcast message from bozo (pts/1) Sun Jul 8 13:53:27 2001... System going down for maintenance in 5 minutes!
If write access to a particular terminal has been disabled with mesg, then wall cannot send a message to it.
- dmesg
Lists all system bootup messages to stdout. Handy for debugging and ascertaining which device drivers were installed and which system interrupts in use. The output of dmesg may, of course, be parsed with grep, sed, or awk from within a script.
bash$ dmesg | grep hda Kernel command line: ro root=/dev/hda2 hda: IBM-DLGA-23080, ATA DISK drive hda: 6015744 sectors (3080 MB) w/96KiB Cache, CHS=746/128/63 hda: hda1 hda2 hda3 < hda5 hda6 hda7 > hda4
- uname
Output system specifications (OS, kernel version, etc.) to stdout. Invoked with the -a option, gives verbose system info (see Example 12-5). The -s option shows only the OS type.
bash$ uname -a Linux localhost.localdomain 2.2.15-2.5.0 #1 Sat Feb 5 00:13:43 EST 2000 i686 unknown bash$ uname -s Linux
- arch
Show system architecture. Equivalent to uname -m. See Example 10-26.
bash$ arch i686 bash$ uname -m i686
- lastcomm
Gives information about previous commands, as stored in the /var/account/pacct file. Command name and user name can be specified by options. This is one of the GNU accounting utilities.
- lastlog
List the last login time of all system users. This references the /var/log/lastlog file.
bash$ lastlog root tty1 Fri Dec 7 18:43:21 -0700 2001 bin **Never logged in** daemon **Never logged in** ... bozo tty1 Sat Dec 8 21:14:29 -0700 2001 bash$ lastlog | grep root root tty1 Fri Dec 7 18:43:21 -0700 2001
This command will fail if the user invoking it does not have read permission for the /var/log/lastlog file.
- lsof
List open files. This command outputs a detailed table of all currently open files and gives information about their owner, size, the processes associated with them, and more. Of course, lsof may be piped to grep and/or awk to parse and analyze its results.
bash$ lsof COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME init 1 root mem REG 3,5 30748 30303 /sbin/init init 1 root mem REG 3,5 73120 8069 /lib/ld-2.1.3.so init 1 root mem REG 3,5 931668 8075 /lib/libc-2.1.3.so cardmgr 213 root mem REG 3,5 36956 30357 /sbin/cardmgr ...
- strace
Diagnostic and debugging tool for tracing system calls and signals. The simplest way of invoking it is strace COMMAND.
bash$ strace df execve("/bin/df", ["df"], [/* 45 vars */]) = 0 uname({sys="Linux", node="bozo.localdomain", ...}) = 0 brk(0) = 0x804f5e4 ...This is the Linux equivalent of truss.
- nmap
Network port scanner. This command scans a server to locate open ports and the services associated with those ports. It is an important security tool for locking down a network against hacking attempts.
1 #!/bin/bash 2 3 SERVER=$HOST # localhost.localdomain (127.0.0.1). 4 PORT_NUMBER=25 # SMTP port. 5 6 nmap $SERVER | grep -w "$PORT_NUMBER" # Is that particular port open? 7 # grep -w matches whole words only, 8 #+ so this wouldn't match port 1025, for example. 9 10 exit 0 11 12 # 25/tcp open smtp
- free
Shows memory and cache usage in tabular form. The output of this command lends itself to parsing, using grep, awk or Perl. The procinfo command shows all the information that free does, and much more.
bash$ free total used free shared buffers cached Mem: 30504 28624 1880 15820 1608 16376 -/+ buffers/cache: 10640 19864 Swap: 68540 3128 65412To show unused RAM memory:
bash$ free | grep Mem | awk '{ print $4 }' 1880- procinfo
Extract and list information and statistics from the /proc pseudo-filesystem. This gives a very extensive and detailed listing.
bash$ procinfo | grep Bootup Bootup: Wed Mar 21 15:15:50 2001 Load average: 0.04 0.21 0.34 3/47 6829
- lsdev
List devices, that is, show installed hardware.
bash$ lsdev Device DMA IRQ I/O Ports ------------------------------------------------ cascade 4 2 dma 0080-008f dma1 0000-001f dma2 00c0-00df fpu 00f0-00ff ide0 14 01f0-01f7 03f6-03f6 ...
- du
Show (disk) file usage, recursively. Defaults to current working directory, unless otherwise specified.
bash$ du -ach 1.0k ./wi.sh 1.0k ./tst.sh 1.0k ./random.file 6.0k . 6.0k total
- df
Shows filesystem usage in tabular form.
bash$ df Filesystem 1k-blocks Used Available Use% Mounted on /dev/hda5 273262 92607 166547 36% / /dev/hda8 222525 123951 87085 59% /home /dev/hda7 1408796 1075744 261488 80% /usr
- stat
Gives detailed and verbose statistics on a given file (even a directory or device file) or set of files.
bash$ stat test.cru File: "test.cru" Size: 49970 Allocated Blocks: 100 Filetype: Regular File Mode: (0664/-rw-rw-r--) Uid: ( 501/ bozo) Gid: ( 501/ bozo) Device: 3,8 Inode: 18185 Links: 1 Access: Sat Jun 2 16:40:24 2001 Modify: Sat Jun 2 16:40:24 2001 Change: Sat Jun 2 16:40:24 2001
If the target file does not exist, stat returns an error message.
bash$ stat nonexistent-file nonexistent-file: No such file or directory
- vmstat
Display virtual memory statistics.
bash$ vmstat procs memory swap io system cpu r b w swpd free buff cache si so bi bo in cs us sy id 0 0 0 0 11040 2636 38952 0 0 33 7 271 88 8 3 89- netstat
Show current network statistics and information, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain bash$ echo $HOSTNAME localhost.localdomain
Similar to the hostname command are the domainname, dnsdomainname, nisdomainname, and ypdomainname commands. Use these to display or set the system DNS or NIS/YP domain name. Various options to hostname also perform these functions.
- hostid
Echo a 32-bit hexadecimal numerical identifier for the host machine.
bash$ hostid 7f0100
This command allegedly fetches a "unique" serial number for a particular system. Certain product registration procedures use this number to brand a particular user license. Unfortunately, hostid only returns the machine network address in hexadecimal, with pairs of bytes transposed.
The network address of a typical non-networked Linux machine, is found in /etc/hosts.
bash$ cat /etc/hosts 127.0.0.1 localhost.localdomain localhost
As it happens, transposing the bytes of 127.0.0.1, we get 0.127.1.0, which translates in hex to 007f0100, the exact equivalent of what hostid returns, above. There exist only a few million other Linux machines with this identical hostid.
- sar
Invoking sar (System Activity Reporter) gives a very detailed rundown on system statistics. The Santa Cruz Operation (SCO) released sar as Open Source in June, 1999.
This command is not part of the base Linux distribution, but may be obtained as part of the sysstat utilities package, written by Sebastien Godard.
bash$ sar Linux 2.4.9 (brooks.seringas.fr) 09/26/03 10:30:00 CPU %user %nice %system %iowait %idle 10:40:00 all 2.21 10.90 65.48 0.00 21.41 10:50:00 all 3.36 0.00 72.36 0.00 24.28 11:00:00 all 1.12 0.00 80.77 0.00 18.11 Average: all 2.23 3.63 72.87 0.00 21.27 14:32:30 LINUX RESTART 15:00:00 CPU %user %nice %system %iowait %idle 15:10:00 all 8.59 2.40 17.47 0.00 71.54 15:20:00 all 4.07 1.00 11.95 0.00 82.98 15:30:00 all 0.79 2.94 7.56 0.00 88.71 Average: all 6.33 1.70 14.71 0.00 77.26- readelf
Show information and statistics about a designated elf binary. This is part of the binutils package.
bash$ readelf -h /bin/bash ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: EXEC (Executable file) . . .
- size
The size [/path/to/binary] command gives the segment sizes of a binary executable or archive file. This is mainly of use to programmers.
bash$ size /bin/bash text data bss dec hex filename 495971 22496 17392 535859 82d33 /bin/bash
- logger
Appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger. n, such as routing tables and active connections. This utility accesses information in /proc/net (Chapter 28). See Example 28-3.
netstat -r is equivalent to route.
bash$ netstat Active Internet connections (w/o servers) Proto Recv-Q Send-Q Local Address Foreign Address State Active UNIX domain sockets (w/o servers) Proto RefCnt Flags Type State I-Node Path unix 11 [ ] DGRAM 906 /dev/log unix 3 [ ] STREAM CONNECTED 4514 /tmp/.X11-unix/X0 unix 3 [ ] STREAM CONNECTED 4513 . . .
- uptime
Shows how long the system has been running, along with associated statistics.
bash$ uptime 10:28pm up 1:57, 3 users, load average: 0.17, 0.34, 0.27
- hostname
Lists the system's host name. This command sets the host name in an /etc/rc.d setup script (/etc/rc.d/rc.sysinit or similar). It is equivalent to uname -n, and a counterpart to the $HOSTNAME internal variable.
bash$ hostname localhost.localdomain