Linux Commands

Commands A-H

arch Outputs the processor architecture.

$ arch

i686 cat Outputs the contents of a file.

$ cat lorem.txt

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. cd Change the working directory.

$ cd /bin chgrp Change group ownership of files.

$ chgrp games moo.txt chmod Change access permissions of files.

$ chmod +x helloworld chown Change file owner and group.

# chown root lorem.txt cksum Print CRC checksum and byte counts of each file.

$ cksum lorem.txt moo.txt

3570240675 453 lorem.txt 4294967295 0 moo.txt cp Copies a file.

$ cp lorem.txt copy_of_lorem.txt date Outputs the current date and time.

$ date

Sat Mar 3 12:07:09 GMT 2007 df Reports the amount of disk space used and available on filesystems.

$ df

Filesystem 1K-blocks Used Available Use% Mounted on<br> /dev/simfs 39845888 218048 39627840 1% / dir List directory contents.

$ dir

copy_of_lorem.txt lorem.txt moo.txt www du Estimate file space usage.

$ du -h /bin

7.8M /bin echo Display a line of text.

$ echo foobar

foobar exit Cause the shell to exit.

$ exit fgrep Print lines matching a pattern in a file.

$ fgrep “irure dolor” lorem.txt

commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
find Search for files in a directory hierarchy.

$ find hello*

hello_world hello_world.c free Display amount of free and used memory in the system.

$ free

total used free shared buffers cached Mem: 8299892 8287708 12184 0 2641772 1731236 Low: 3581300 3572764 8536 High: 4718592 4714944 3648
-/+ buffers/cache: 3914700 4385192 Swap: 8193140 2335664 5857476
grep Print lines matching a pattern.

$ grep -i apple fruitlist.txt

apple groups Outputs the user groups of which your account belongs to.

$ groups

games users head Output the first part of files.

$ head -2 lorem.txt

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
hostname Outputs the machines hostname on the network.

$ hostname

anapnea.net

Commands I-N

id Outputs user id, group id, and groups of your account.

$ id

uid=1478(smallfoot) gid=100(users) groups=35(games),100(users) kill
End a process.

$ kill -9 18298

-bash: kill: (18298) – Operation not permitted killall Kill processes by name.

$ killall irssi

irssi(18298): Operation not permitted irssi(13372): Operation not permitted irssi(22048): Operation not permitted irssi: no process killed
last Show listing of last logged in users.

$ last -n 3

alice pts/6 192.0.34.166 Fri May 18 16:17 still logged in bob pts/2 64.233.183.103 Fri May 18 16:17 still logged in clare pts/6 72.5.124.61 Fri May 18 15:54 – 15:55 (00:01) ldd Print shared library dependencies.

$ ldd /bin/bash

libncurses.so.5 => /lib/libncurses.so.5 (0×40023000) libdl.so.2 => /lib/libdl.so.2 (0×40065000) libc.so.6 => /lib/libc.so.6 (0×40069000)
/lib/ld-linux.so.2 (0×40000000) ln Make links between files.

$ ln -s data.txt symlink.txt logname Print user’s login name.

$ logname

smallfoot ls List directory contents.

$ ls

copy_of_lorem.txt lorem.txt moo.txt www man Opens the manual page for a software or function.

$ man bash md5sum Outputs the MD5 hash sum of a file.

$ md5sum lorem.txt

56da9e37259af34345895883e6fd1a27 lorem.txt mkdir Makes a directory.

$ mkdir foobar mv Moves a file.

$ mv lorem.txt ipsum.txt nl Number lines of files.

$ nl lorem.txt

1 Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
2 tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim 3 veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea 4 commodo consequat. Duis aute irure dolor in reprehenderit in voluptate 5 velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint 6 occaecat cupidatat non proident, sunt in culpa qui officia deserunt 7 mollit anim id est laborum. nm List symbols from object files.

$ nm hello_world

080494a0 D _DYNAMIC 0804956c D _GLOBAL_OFFSET_TABLE_ 08048474 R _IO_stdin_used w _Jv_RegisterClasses 08049490 d __CTOR_END__
0804948c d __CTOR_LIST__ 08049498 d __DTOR_END__ …

Commands O-S

od Dump files in octal and other formats.

$ od -t x /bin/sh

2376640 00098020 000054d4 00000000 00000000 2376660 00000020 00000000 000000c7 00000008 2376700 00000003 080e6500 0009d4f4 00004ae8 …
pidof Find the process ID of a running program.

$ pidof fetchmail

22392 ping Pings a host.

$ ping -c 2 127.0.0.1

PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data. 64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.048 ms 64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.052 ms

— 127.0.0.1 ping statistics — 2 packets transmitted, 2 received, 0% packet loss, time 999ms rtt min/avg/max/mdev = 0.048/0.050/0.052/0.002 ms
ps Outputs running processes.

$ ps

PID TTY TIME CMD 21542 pts/12 00:00:00 bash 27706 pts/12 00:00:00 ps
pstree Display a tree of processes.

$ pstree

init-+-2*[BitchX] |-3*[bash---sleep] |-fetchmail
|-screen-+-bash—irssi | `-bash—ctorrent
|-screen-+-bash—lisp.run | |-bash—vi | |-2*[bash] | `-bash—lynx |-2*[screen---bash---irssi] |-screen—irssi
|-screen—bash |-screen-+-bash | `-irssi |-skjerm—irssi
|-sshd-+-5*[sshd---sshd---bash---irssi] | |-8*[sshd---sshd---bash] | |-sshd—sshd—bash—screen | |-sshd—sshd | `-sshd—sshd—bash—pstree `-syslog-ng pwd Outputs the name of current working directory.

$ pwd

/home/smallfoot rm Removes a file or directory.

$ rm lorem.txt rmdir Removes a directory.

$ rmdir foobar sed Stream editor for filtering and transforming text.

$ echo “My cat’s name is Bob” | sed -e ‘s/Bob/Mittens/g’

My cat’s name is Mittens sha1sum Outputs the SHA1 hash sum of a file.

$ sha1sum lorem.txt

c942ddebd142ec8bacac9213d48096e74bab4957 lorem.txt shutdown Bring the system down in a secure way. All logged-in users are notified that the system is going down.

$ shutdown now size List section sizes and total size.

$ size /bin/bash

text data bss dec hex filename 621233 22712 19176 663121 a1e51 /bin/bash
stat Outputs file status.

$ stat lorem.txt

File: `lorem.txt’ Size: 453 Blocks: 8 IO Block: 4096 regular file
Device: 77h/119d Inode: 27312217 Links: 1 Access: (0644/-rw-r–r–) Uid: ( 1478/smallfoot) Gid: ( 100/ users) Access: 2007-03-03 12:24:39.000000000 +0000 Modify: 2007-03-03 12:24:39.000000000 +0000 Change: 2007-03-03 12:24:39.000000000 +0000 strings Print the strings of printable characters in files.

$ strings hello_world

/lib/ld-linux.so.2 _Jv_RegisterClasses __gmon_start__ libc.so.6
puts _IO_stdin_used __libc_start_main GLIBC_2.0 PTRh%
[^_] Hello World!

Commands T-W

tail Output the last part of files.

$ tail -2 lorem.txt

occaecat cupidatat non proident, sunt in culpa qui officia deserunt
mollit anim id est laborum. talk Talk to another user.

$ talk bob Lookout for the dopefish! touch Change a file’s access and modification timestamps. If file does not exist, create it.

$ touch lorem.txt tty Outputs the name of the current terminal.

$ tty

/dev/pts/16 uname Outputs operating system, hostname, kernel version, date and timp, and processor.

$ uname -a

Linux anapnea.net 2.6.9 #1 SMP Wed Jul 19 16:24:18 MSD 2006 i686 Intel(R) Xeon(TM) CPU 2.80GHz GenuineIntel GNU/Linux uptime Outputs the system uptime.

$ uptime

14:50:26 up 7 days, 17:52, 18 users, load average: 0.08, 0.02, 0.01 users
Print the user names of users currently logged in to the current host.

$ users

alice bob charlie eve vdir List directory contents.

$ vdir

total 8 -rw-r–r– 1 smallfoot users 453 Mar 3 12:32 copy_of_lorem.txt
-rw-r–r– 1 smallfoot users 453 Mar 3 12:24 lorem.txt -rw-r–r– 1 smallfoot users 0 Mar 3 12:32 moo.txt lrwxr-xr-x 1 root root 18 Feb 27 19:33 www -> /var/www/smallfoot w Show who is logged on and what they are doing.

$ w

12:14:30 up 5 days, 15:16, 19 users, load average: 0.00, 0.00, 0.00 USER TTY LOGIN@ IDLE JCPU PCPU WHAT charlie pts/0 Fri21 3:26m 2.52s 2.52s irssi
alice pts/2 Wed17 30:21m 0.00s 0.00s -bash emma pts/4 11:37 36:57 0.00s 0.00s -bash frank pts/5 11:48 11:03 0.00s 0.00s -bash smallfoo pts/12 12:01 0.00s 0.04s 0.01s w wall Send a message to everybody’s terminal.

$ wall next week we change the server for a new one wc Counts lines in a file.

$ wc -l lorem.txt

7 lorem.txt whatis Search the whatis database for complete words.

$ whatis bash

bash (1) – GNU Bourne-Again SHell bash [builtins] (1) – bash built-in commands, see bash(1) who Outputs who is currently logged into the system.

$ who

charlie pts/0 Mar 2 21:37 (xtreme-11-65.acme.com) alice pts/2 Feb 28 17:48 (147.21.16.3) emma pts/4 Mar 3 11:37 (32.84-48-181.uac.com) frank pts/5 Mar 3 11:48 (port-212-202-233-2.foobar.org) smallfoot pts/12 Mar 3 12:01 (c-12776f4.cust.example.net) whereis Locate the binary, source, and manual page files for a command.

$ whereis bash

bash: /bin/bash /etc/bash /usr/share/man/man1/bash.1.gz whoami
Outputs your username / the name of your account.

$ whoami

smallfoot