Useful commands for the Linux command line

This short guide shows some important commands for your daily work on the Linux command line.

• 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
  /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
  Remove ads

• 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

  123tweak.com

• 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 foldername

• mv
  Moves a file.

  $ mv post.txt newpost.txt

• nl
  Number lines of files.

  $ nl post.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__
  …

• 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 foldername

• 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!

• 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

  root bob charlie frank

• 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 post.txt

  7 post.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