UNIX/LINUX COMMANDS

admin - create and administer SCCS files (DEVELOPMENT)
alias - define or display aliases
ar - create and maintain library archives
asa - interpret carriage-control characters
at - execute commands at a later time
awk - pattern scanning and processing language
basename - return non-directory portion of a pathname
batch - schedule commands to be executed in a batch queue
bc - arbitrary-precision arithmetic language
bg - run jobs in the background
c99 - compile standard C programs
cal - print a calendar
cat - concatenate and print files
cd - change the working directory
cflow - generate a C-language flowgraph (DEVELOPMENT)
chgrp - change the file group ownership
chmod - change the file modes
chown - change the file ownership
cksum - write file checksums and sizes
cmp - compare two files
command - execute a simple command
comm - select or reject lines common to two files
compress - compress data
cp - copy files
crontab - schedule periodic background work
csplit - split files based on context
ctags - create a tags file (DEVELOPMENT, FORTRAN)
cut - cut out selected fields of each line of a file
cxref - generate a C-language program cross-reference table
(DEVELOPMENT)
date - write the date and time
dd - convert and copy a file
delta - make a delta (change) to an SCCS file (DEVELOPMENT)
df - report free disk space
diff - compare two files
dirname - return the directory portion of a pathname
du - estimate file space usage
echo - write arguments to standard output
ed - edit text
env - set the environment for command invocation
ex - text editor
expand - convert tabs to spaces
expr - evaluate arguments as an expression
false - return false value
fc - process the command history list
fg - run jobs in the foreground
file - determine file type
find - find files
fold - filter for folding lines
fort77 - FORTRAN compiler (FORTRAN)
fuser - list process IDs of all processes that have one or more files
open
gencat - generate a formatted message catalog
getconf - get configuration values
get - get a version of an SCCS file (DEVELOPMENT)
getopts - parse utility options
grep - search a file for a pattern
hash - remember or report utility locations
head - copy the first part of files
iconv - codeset conversion
id - return user identity
ipcrm - remove an XSI message queue, semaphore set, or shared memory
segment identifier
ipcs - report XSI interprocess communication facilities status
jobs - display status of jobs in the current session
join - relational database operator
kill - terminate or signal processes
lex - generate programs for lexical tasks (DEVELOPMENT)
link - call link function
ln - link files
localedef - define locale environment
locale - get locale-specific information
logger - log messages
logname - return the user's login name
lp - send files to a printer
ls - list directory contents
m4 - macro processor
mailx - process messages
make - maintain, update, and regenerate groups of programs
(DEVELOPMENT)
man - display system documentation
mesg - permit or deny messages
mkdir - make directories
mkfifo - make FIFO special files
more - display files on a page-by-page basis
mv - move files
newgrp - change to a new group
nice - invoke a utility with an altered nice value
nl - line numbering filter
nm - write the name list of an object file (DEVELOPMENT)
nohup - invoke a utility immune to hangups
od - dump files in various formats
paste - merge corresponding or subsequent lines of files
patch - apply changes to files
pathchk - check pathnames
pax - portable archive interchange
pr - print files
printf - write formatted output
prs - print an SCCS file (DEVELOPMENT)
ps - report process status
pwd - return working directory name
qalter - alter batch job
qdel - delete batch jobs
qhold - hold batch jobs
qmove - move batch jobs
qmsg - send message to batch jobs
qrerun - rerun batch jobs
qrls - release batch jobs
qselect - select batch jobs
qsig - signal batch jobs
qstat - show status of batch jobs
qsub - submit a script
read - read from standard input into shell variables
renice - set nice values of running processes
rmdel - remove a delta from an SCCS file (DEVELOPMENT)
rmdir - remove directories
rm - remove directory entries
sact - print current SCCS file-editing activity (DEVELOPMENT)
sccs - front end for the SCCS subsystem (DEVELOPMENT)
sed - stream editor
sh - shell, the standard command language interpreter
sleep - suspend execution for an interval
sort - sort, merge, or sequence check text files
split - split a file into pieces
strings - find printable strings in files
strip - remove unnecessary information from strippable files
(DEVELOPMENT)
stty - set the options for a terminal
tabs - set terminal tabs
tail - copy the last part of a file
talk - talk to another user
tee - duplicate standard input
test - evaluate expression
time - time a simple command
touch - change file access and modification times
tput - change terminal characteristics
tr - translate characters
true - return true value
tsort - topological sort
tty - return user's terminal name
type - write a description of command type
ulimit - set or report file size limit
umask - get or set the file mode creation mask
unalias - remove alias definitions
uname - return system name
uncompress - expand compressed data
unexpand - convert spaces to tabs
unget - undo a previous get of an SCCS file (DEVELOPMENT)
uniq - report or filter out repeated lines in a file
unlink - call the unlink function
uucp - system-to-system copy
uudecode - decode a binary file
uuencode - encode a binary file
uustat - uucp status enquiry and job control
uux - remote command execution
val - validate SCCS files (DEVELOPMENT)
vi - screen-oriented (visual) display editor
wait - await process completion
wc - word, line, and byte or character count
what - identify SCCS files (DEVELOPMENT)
who - display who is on the system
write - write to another user
xargs - construct argument lists and invoke utility
yacc - yet another compiler compiler (DEVELOPMENT)
zcat - expand and concatenate data

Linux Commands – A
Command Description
accept Accept or Reject jobs to a destination, such as a printer.
access Check a user’s RWX permission for a file.
aclocal GNU autoconf too
aconnect ALSA sequencer connection manager.
acpi Show information about the Advanced Configuration and Power Interface.
acpiavailable Check if ACPI functionality exists on the system.
acpid Informs user-space programs about ACPI events.
addr2line Used to convert addresses into file names and line numbers.
addresses Formats for internet mail addresses.
agetty An alternative Linux Getty
alias Create an alias for Linux commands
alsactl Access advanced controls for ALSA soundcard driver.
amidi Perform read/write operation for ALSA RawMIDI ports.
amixer Access CLI-based mixer for ALSA soundcard driver.
anacron Used to run commands periodically.
aplay Sound recorder and player for CLI.
aplaymidi CLI utility used to play MIDI files.
apm Show Advanced Power Management (APM) hardware info on older systems.
apmd Used to handle events reported by APM BIOS drivers.
apropos Shows the list of all man pages containing a specific keyword
apt Advanced Package Tool, a package management system for Debian and derivatives.
apt-get Command-line utility to install/remove/update packages based on APT system.
aptitude Another utility to add/remove/upgrade packages based on the APT system.
ar A utility to create/modify/extract from archives.
arch Display print machine hardware name.
arecord Just like aplay, it’s a sound recorder and player for ALSA soundcard driver.
arecordmidi Record standard MIDI files.
arp Used to make changes to the system’s ARP cache
as A portable GNU assembler.
aspell An interactive spell checker utility.
at Used to schedule command execution at specified date & time, reading commands from an input file.
atd Used to execute jobs queued by the at command.
atq List a user’s pending jobs for the at command.
atrm Delete jobs queued by the at command.
audiosend Used to send an audio recording as an email.
aumix An audio mixer utility.
autoconf Generate configuration scripts from a TEMPLATE-FILE and send the output to standard output.
autoheader Create a template header for configure.
automake Creates GNU standards-compliant Makefiles from template files
autoreconf Update generated configuration files.
autoscan Generate a preliminary configure.in
autoupdate Update a configure.in file to newer autoconf.
awk Used to find and replace text in a file(s).
Linux Commands – B
Command Description
badblocks Search a disk partition for bad sectors.
banner Used to print characters as a poster.
basename Used to display filenames with directoy or suffix.
bash GNU Bourne-Again Shell.
batch Used to run commands entered on a standard input.
bc Access the GNU bc calculator utility.
bg Send processes to the background.
biff Notify about incoming mail and sender’s name on a system running comsat server.
bind Used to attach a name to a socket.
bison A GNU parser generator, compatible with yacc.
break Used to exit from a loop (eg: for, while, select).
builtin Used to run shell builtin commands, make custom functions for commands extending their functionality.
bzcmp Used to call the cmp program for bzip2 compressed files.
bzdiff Used to call the diff program for bzip2 compressed files.
bzgrep Used to call grep for bzip2 compressed files.
bzip2 A block-sorting file compressor used to shrink given files.
bzless Used to apply ‘less’ (show info one page at a time) to bzip2 compressed files.
bzmore Used to apply ‘more’ (an inferior version of less) to bzip2 compressed files.
Linux Commands – C
Command Description
cal Show calendar.
cardctl Used to control PCMCIA sockets and select configuration schemes.
cardmgr Keeps an eye on the added/removes sockets for PCMCIA devices.
case Execute a command conditionally by matching a pattern.
cat Used to concatenate files and print them on the screen.
cc GNU C and C++ compiler.
cd Used to change directory.
cdda2wav Used to rip a CD-ROM and make WAV file.
cdparanoia Record audio from CD more reliably using data-verification algorithms.
cdrdao Used to write all the content specified to a file to a CD all at once.
cdrecord Used to record data or audio compact discs.
cfdisk Show or change the disk partition table.
chage Used to change user password information.
chattr Used to change file attributes.
chdir Used to change active working directory.
chfn Used to change real user name and information.
chgrp Used to change group ownership for file.
chkconfig Manage execution of runlevel services.
chmod Change access permission for a file(s).
chown Change the owner or group for a file.
chpasswd Update password in a batch.
chroot Run a command with root privileges.
chrt Alter process attributed in real-time.
chsh Switch login shell.
chvt Change foreground virtual terminal.
cksum Perform a CRC checksum for files.
clear Used to clear the terminal window.
cmp Compare two files (byte by byte).
col Filter reverse (and half-reverse) line feeds from the input.
colcrt Filter nroff output for CRT previewing.
colrm Remove columns from the lines of a file.
column A utility that formats its input into columns.
comm Used to compare two sorted files line by line.
command Used to execute a command with arguments ignoring shell function named command.
compress Used to compress one or more file(s) and replacing the originals ones.
continue Resume the next iteration of a loop.
cp Copy contents of one file to another.
cpio Copy files from and to archives.
cpp GNU C language processor.
cron A daemon to execute scheduled commands.
crond Same work as cron.
crontab Manage crontab files (containing schedules commands) for users.
csplit Split a file into sections on the basis of context lines.
ctags Make a list of functions and macro names defined in a programming source file.
cupsd A scheduler for CUPS.
curl Used to transfer data from or to a server using supported protocols.
cut Used to remove sections from each line of a file(s).
cvs Concurrent Versions System. Used to track file versions, allow storage/retrieval of previous versions, and enables multiple users to work on the same file.
Linux Commands – D
Command Description
date Show system date and time.
dc Desk calculator utility.
dd Used to convert and copy a file, create disk clone, write disk headers, etc.
ddrescue Used to recover data from a crashed partition.
deallocvt Deallocates kernel memory for unused virtual consoles.
debugfs File system debugger for ext2/ext3/ext4
declare Used to declare variables and assign attributes.
depmod Generate modules.dep and map files.
devdump Interactively displays the contents of device or file system ISO.
df Show disk usage.
diff Used to compare files line by line.
diff3 Compare three files line by line.
dig Domain Information Groper, a DNS lookup utility.
dir List the contents of a directory.
dircolors Set colors for ‘ls’ by altering the LSCOLORS environment variable.
dirname Display pathname after removing the last slash and characters thereafter.
dirs Show the list of remembered directories.
disable Restrict access to a printer.
dlpsh Interactive Desktop Link Protocol (DLP) shell for PalmOS.
dmesg Examine and control the kernel ring buffer.
dnsdomainname Show the DNS domain name of the system.
dnssec-keygen Generate encrypted Secure DNS keys for a given domain name.
dnssec-makekeyset Produce domain key set from one or more DNS security keys generated by dnssec-keygen.
dnssec-signkey Sign a secure DNS keyset with key signatures specified in the list of key-identifiers.
dnssec-signzone Sign a secure DNS zonefile with the signatures in the specified list of key-identifiers.
doexec Used to run an executable with an arbitrary argv list provided.
domainname Show or set the name of current NIS (Network Information Services) domain.
dosfsck Check and repair MS-DOS file systems.
du Show disk usage summary for a file(s).
dump Backup utility for ext2/ext3 file systems.
dumpe2fs Dump ext2/ext3/ext4 file systems.
dumpkeys Show information about the keyboard driver’s current translation tables.
Linux Commands – E
Command Desription
e2fsck Used to check ext2/ext3/ext4 file systems.
e2image Store important ext2/ext3/ext4 filesystem metadata to a file.
e2label Show or change the label on an ext2/ext3/ext4 filesystem.
echo Send input string(s) to standard output i.e. display text on the screen.
ed GNU Ed – a line-oriented text editor.
edquota Used to edit filesystem quotas using a text editor, such as vi.
egrep Search and display text matching a pattern.
eject Eject removable media.
elvtune Used to set latency in the elevator algorithm used to schedule I/O activities for specified block devices.
emacs Emacs text editor command line utility.
enable Used to enable/disable shell builtin commands.
env Run a command in a modified environment. Show/set/delete environment variables.
envsubst Substitute environment variable values in shell format strings.
esd Start the Enlightenment Sound Daemon (EsounD or esd). Enables multiple applications to access the same audio device simultaneously.
esd-config Manage EsounD configuration.
esdcat Use EsounD to send audio data from a specified file.
esdctl EsounD control program.
esddsp Used to reroute non-esd audio data to esd and control all the audio using esd.
esdmon Used to copy the sound being sent to a device. Also, send it to a secondary device.
esdplay Use EsounD system to play a file.
esdrec Use EsounD to record audio to a specified file.
esdsample Sample audio using esd.
etags Used to create a list of functions and macros from a programming source file. These etags are used by emacs. For vi, use ctags.
ethtool Used to query and control network driver and hardware settings.
eval Used to evaluate multiple commands or arguments are once.
ex Interactive command
exec An interactive line-based text editor.
exit Exit from the terminal.
expand Convert tabs into spaces in a given file and show the output.
expect An extension to the Tcl script, it’s used to automate interaction with other applications based on their expected output.
export Used to set an environment variable.
expr Evaluate expressions and display them on standard output.
Linux Commands – F
Command Description
factor Display prime factors of specified integer numbers.
false Do nothing, unsuccessfully. Exit with a status code indicating failure.
fc-cache Make font information cache after scanning the directories.
fc-list Show the list of available fonts.
fdformat Do a low-level format on a floppy disk.
fdisk Make changes to the disk partition table.
fetchmail Fetch mail from mail servers and forward it to the local mail delivery system.
fg Used to send a job to the foreground.
fgconsole Display the number of the current virtual console.
fgrep Display lines from a file(s) that match a specified string. A variant of grep.
file Determine file type for a file.
find Do a file search in a directory hierarchy.
finger Display user data including the information listed in .plan and .project in each user’s home directory.
fingerd Provides a network interface for the finger program.
flex Generate programs that perform pattern-matching on text.
fmt Used to convert text to a specified width by filling lines and removing new lines, displaying the output.
fold Wrap input line to fit in a specified width.
for Expand words and run commands for each one in the resultant list.
formail Used to filter standard input into mailbox format.
format Used to format disks.
free Show free and used system memory.
fsck Check and repair a Linux file system
ftp File transfer protocol user interface.
ftpd FTP server process.
function Used to define function macros.
fuser Find and kill a process accessing a file.
Linux Commands – G
Command Description
g++ Run the g++ compiler.
gawk Used for pattern scanning and language processing. A GNU implementation of AWK language.
gcc A C and C++ compiler by GNU.
gdb A utility to debug programs and know about where it crashes.
getent Shows entries from Name Service Switch Libraries for specified keys.
getkeycodes Displays the kernel scancode-to-keycode mapping table.
getopts A utility to parse positional parameters.
gpasswd Allows an administrator to change group passwords.
gpg Enables encryption and signing services as per the OpenPGP standard.
gpgsplit Used to split an OpenPGP message into packets.
gpgv Used to verify OpenPGP signatures.
gpm It enables cut and paste functionality and a mouse server for the Linux console.
gprof Shows call graph profile data.
grep Searches input files for a given pattern and displays the relevant lines.
groff Serves as the front-end of the groff document formatting system.
groffer Displays groff files and man pages.
groupadd Used to add a new user group.
groupdel Used to remove a user group.
groupmod Used to modify a group definition.
groups Show the group(s) to which a user belongs.
grpck Verifies the integrity of group files.
grpconv Creates a gshadow file from a group or an already existing gshadow.
gs Invokes Ghostscript, and interpreter and previewer for Adobe’s PostScript and PDF languages.
gunzip A utility to compress/expand files.
gzexe Used compress executable files in place and have them automatically uncompress and run at a later stage.
gzip Same as gzip.
Linux Commands – H
Command Description
halt Command used to half the machine.
hash Shows the path for the commands executed in the shell.
hdparm Show/configure parameters for SATA/IDE devices.
head Shows first 10 lines from each specified file.
help Display’s help for a built-in command.
hexdump Shows specified file output in hexadecimal, octal, decimal, or ASCII format.
history Shows the command history.
host A utility to perform DNS lookups.
hostid Shows host’s numeric ID in hexadecimal format.
hostname Display/set the hostname of the system.
htdigest Manage the user authentication file used by the Apache web server.
htop An interactive process viewer for the command line.
hwclock Show or configure the system’s hardware clock.
Linux Commands – I
Command Description
iconv Convert text file from one encoding to another.
id Show user and group information for a specified user.
if Execute a command conditionally.
ifconfig Used to configure network interfaces.
ifdown Stops a network interface.
ifup Starts a network interface.
imapd An IMAP (Interactive Mail Access Protocol) server daemon.
import Capture an X server screen and saves it as an image.
inetd Extended internet services daemon, it starts the programs that provide internet services.
info Used to read the documentation in Info format.
init Systemd system and service manager.
insmod A program that inserts a module into the Linux kernel.
install Used to copy files to specified locations and set attributions during the install process.
iostat Shows statistics for CPU, I/O devices, partitions, network filesystems.
ip Display/manipulate routing, devices, policy, routing and tunnels.
ipcrm Used to remove System V interprocess communication (IPC) objects and associated data structures.
ipcs Show information on IPC facilities for which calling process has read access.
iptables Administration tool for IPv4 packet filtering and NAT.
iptables-restore Used to restore IP tables from data specified in the input or a file.
iptables-save Used to dump IP table contents to standard output.
isodump A utility that shows the content iso9660 images to verify the integrity of directory contents.
isoinfo A utility to perform directory like listings of iso9660 images.
isosize Show the length of an iso9660 filesystem contained in a specified file.
isovfy Verifies the integrity of an iso9660 image.
ispell A CLI-based spell-check utility.
Linux Commands – J
Command Description
jobs Show the list of active jobs and their status.
join For each pair of input lines, join them using a command field and display on standard output.
Linux Commands – K
Command Description
kbdmode Set a keyboard mode. Without arguments, shows the current keyboard mode.
kbdrate Reset keyboard repeat rate and delay time.
kill Send a kill (termination) signal to one more processes.
killall Kills a process(es) running a specified command.
killall5 A SystemV killall command. Kills all the processes excluding the ones which it depends on.
klogd Control and prioritize the kernel messages to be displayed on the console, and log them through syslogd.
kudzu Used to detect new and enhanced hardware by comparing it with existing database. Only for RHEL and derivates.
Linux Commands – L
Command Description
last Shows a list of recent logins on the system by fetching data from /var/log/wtmp file.
lastb Shows the list of bad login attempts by fetching data from /var/log/btmp file.
lastlog Displays information about the most recent login of all users or a specified user.
ld The Unix linker, it combines archives and object files. It then puts them into one output file, resolving external references.
ldconfig Configure dynamic linker run-time bindings.
ldd Shows shared object dependencies.
less Displays contents of a file one page at a time. It’s advanced than more command.
lesskey Used to specify key bindings for less command.
let Used to perform integer artithmetic on shell variables.
lftp An FTP utility with extra features.
lftpget Uses lftop to retrieve HTTP, FTP, and other protocol URLs supported by lftp.
link Create links between two files. Similar to ln command.
ln Create links between files. Links can be hard (two names for the same file) or soft (a shortcut of the first file).
loadkeys Load keyboard translation tables.
local Used to create function variables.
locale Shows information about current or all locales.
locate Used to find files by their name.
lockfile Create semaphore file(s) which can be used to limit access to a file.
logger Make entries in the system log.
login Create a new session on the system.
logname Shows the login name of the current user.
logout Performs the logout operation by making changes to the utmp and wtmp files.
logrotate Used for automatic rotation, compression, removal, and mailing of system log files.
look Shows any lines in a file containing a given string in the beginning.
losetup Set up and control loop devices.
lpadmin Used to configure printer and class queues provided by CUPS (Common UNIX Printing System).
lpc Line printer control program, it provides limited control over CUPS printer and class queues.
lpinfo Shows the list of avaiable devices and drivers known to the CUPS server.
lpmove Move on or more printing jobs to a new destination.
lpq Shows current print queue status for a specified printer.
lpr Used to submit files for printing.
lprint Used to print a file.
lprintd Used to abort a print job.
lprintq List the print queue.
lprm Cancel print jobs.
lpstat Displays status information about current classes, jobs, and printers.
ls Shows the list of files in the current directory.
lsattr Shows file attributes on a Linux ext2 file system.
lsblk Lists information about all available or the specified block devices.
lsmod Show the status of modules in the Linux kernel.
lsof List open files.
lspci List all PCI devices.
lsusb List USB devices.
Linux Commands – M
Command Description
m4 Macro processor.
mail Utility to compose, receive, send, forward, and reply to emails.
mailq Shows to list all emails queued for delivery (sendmail queue).
mailstats Shows current mail statistics.
mailto Used to send mail with multimedia content in MIME format.
make Utility to maintain groups of programs, recompile them if needed.
makedbm Creates an NIS (Network Information Services) database map.
makemap Creates database maps used by the keyed map lookups in sendmail.
man Shows manual pages for Linux commands.
manpath Determine search path for manual pages.
mattrib Used to change MS-DOS file attribute flags.
mbadblocks Checks MD-DOS filesystems for bad blocks.
mcat Dump raw disk image.
mcd Used to change MS-DOS directory.
mcopy Used to copy MS-DOS files from or to Unix.
md5sum Used to check MD5 checksum for a file.
mdel, mdeltree Used to delete MS-DOS file. mdeltree recursively deletes MS-DOS directory and its contents.
mdir Used to display an MS-DOS directory.
mdu Used to display the amount of space occupied by an MS-DOS directory.
merge Three-way file merge. Includes all changes from file2 and file3 to file1.
mesg Allow/disallow osends to sedn write messages to your terminal.
metamail For sending and showing rich text or multimedia email using MIME typing metadata.
metasend An interface for sending non-text mail.
mformat Used to add an MS-DOS filesystem to a low-level formatted floppy disk.
mimencode Translate to/from MIME multimedia mail encoding formats.
minfo Display parameters of an MS-DOS filesystem.
mkdir Used to create directories.
mkdosfs Used to create an MS-DOS filesystem under Linux.
mke2fs Used create an ext2/ext3/ext4 filesystem.
mkfifo Used to create named pipes (FIFOs) with the given names.
mkfs Used to build a Linux filesystem on a hard disk partition.
mkfs.ext3 Same as mke2fs, create an ext3 Linux filesystem.
mkisofs Used to create an ISO9660/JOLIET/HFS hybrid filesystem.
mklost+found Create a lost+found directory on a mounted ext2 filesystem.
mkmanifest Makes a list of file names and their DOS 8.3 equivalent.
mknod Create a FIFO, block (buffered) special file, character (unbuffered) special file with the specified name.
mkraid Used to setup RAID device arrays.
mkswap Set up a Linux swap area.
mktemp Create a temporary file or directory.
mlabel Make an MD-DOS volume label.
mmd Make an MS-DOS subdirectory.
mmount Mount an MS-DOS disk.
mmove Move or rename an MS-DOS file or subdirectory.
mmv Mass move and rename files.
modinfo Show information about a Linux kernel module.
modprobe Add or remove modules from the Linux kernel.
more Display content of a file page-by-page.
most Browse or page through a text file.
mount Mount a filesystem.
mountd NFS mount daemon.
mpartition Partition an MS-DOS disk.
mpg123 Command-line mp3 player.
mpg321 Similar to mpg123.
mrd Remove an MS-DOS subdirectory.
mren Rename an existing MS-DOS file.
mshowfat Show FTA clusters allocated to a file.
mt Control magnetic tape drive operation.
mtools Utilities to access MS-DOS disks.
mtoolstest Tests and displays the mtools configuration files.
mtr A network diagnostic tool.
mtype Display contents of an MS-DOS file.
mv Move/rename files or directories.
mzip Change protection mode and eject disk on Zip/Jaz drive.
Linux Commands – N
Command Description
named Internet domain name server.
namei Follow a pathname until a terminal point is found.
nameif Name network interfaces based on MAC addresses.
nc Netcat utility. Arbitrary TCP and UDP connections and listens.
netstat Show network information.
newaliases Rebuilds mail alias database.
newgrp Log-in to a new group.
newusers Update/create new users in batch.
nfsd Special filesystem for controlling Linux NFS server.
nfsstat List NFS statistics.
nice Run a program with modified scheduling priority.
nl Show numbered line while displaying the contents of a file.
nm List symbols from object files.
nohup Run a command immune to hangups.
notify-send A program to send desktop notifications.
nslookup Used performs DNS queries. Read this article for more info.
nsupdate Dynamic DNS update utility.
Linux Commands – O
Command Description
objcopy Copy and translate object files.
objdump Display information from object files.
od Dump files in octal and other formats.
op Operator access, allows system administrators to grant users access to certain root operations that require superuser privileges.
open Open a file using its default application.
openvt Start a program on a new virtual terminal (VT).
Linux Commands – P
Command Description
passwd Change user password.
paste Merge lines of files. Write to standard output, TAB-separated lines consisting of sqentially correspnding lines from each file.
patch Apply a patchfile (containing differences listing by diff program) to an original file.
pathchk Check if file names are valid or portable.
perl Perl 5 language interpreter.
pgrep List process IDs matching the specified criteria among all the running processes.
pidof Find process ID of a running program.
ping Send ICMP ECHOREQUEST to network hosts.
pinky Lightweight finger.
pkill Send kill signal to processes based on name and other attributes.
pmap Report memory map of a process.
popd Removes directory on the head of the directory stack and takes you to the new directory on the head.
portmap Converts RPC program numbers to IP port numbers.
poweroff Shuts down the machine.
pppd Point-to-point protocol daemon.
pr Convert (column or paginate) text files for printing.
praliases Prints the current system mail aliases.
printcap Printer capability database.
printenv Show values of all or specified environment variables.
printf Show arguments formatted according to a specified format.
ps Report a snapshot of the current processes.
ptx Produce a permuted index of file contents.
pushd Appends a given directory name to the head of the stack and then cd to the given directory.
pv Monitor progress of data through a pipe.
pwck Verify integrity of password files.
pwconv Creates shadow from passwd and an optionally existing shadow.
pwd Show current directory.
python

Linux Commands – Q
Command Description
quota Shows disk usage, and space limits for a user or group. Without arguments, only shows user quotas.
quotacheck Used to scan a file system for disk usage.
quotactl Make changes to disk quotas.
quotaoff Enable enforcement of filesystem quotas.
quotaon Disable enforcement of filesystem quotas.
quotastats Shows the report of quota system statistics gathered from the kernel.
Linux Commands – R
Command Description
raidstart Start/stop RAID devices.
ram RAM disk device used to access the RAM disk in raw mode.
ramsize Show usage information for the RAM disk.
ranlib Generate index to the contents of an archive and store it in the archive.
rar Create and manage RAR file in Linux.
rarpd Respond to Reverse Address Resoultion Protocol (RARP) requests.
rcp Remote copy command to copy files between remote computers.
rdate Set system date and time by fetching information from a remote machine.
rdev Set or query RAM disk size, image root device, or video mode.
rdist Remote file distribution client, maintains identical file copies over multiple hosts.
rdistd Start the rdist server.
read Read from a file descriptor.
readarray Read lines from a file into an array variable.
readcd Read/write compact disks.
readelf Shows information about ELF (Executable and Linkable fomrat) files.
readlink Display value of a symbolic link or canonical file name.
readonly Mark functions and variables as read-only.
reboot Restart the machine.
reject Accept/reject print jobs sent to a specified destination.
remsync Synchronize remote files over email.
rename Rename one or more files.
renice Change priority of active processes.
repquota Report disk usage and quotas for a specified filesystem.
reset Reinitialize the terminal.
resize2fs Used to resize ext2/ext3/ext4 file systems.
restore Restore files from a backup created using dump.
return Exit a shell function.
rev Show contents of a file, reversing the order of characters in every line.
rexec Remote execution client for exec server.
rexecd Remote execution server.
richtext View “richtext” on an ACSII terminal.
rlogin Used to connect a local host system with a remote host.
rlogind Acts as the server for rlogin. It facilitates remote login, and authentication based on privileged port numbers from trusted hosts.
rm Removes specified files and directories (not by default).
rmail Handle remote mail received via uucp.
rmdir Used to remove empty directories.
rmmod A program to remove modules from Linux kernel.
rndc Name server control utility. Send command to a BIND DNS server over a TCP connection.
rootflags Show/set flags for the kernel image.
route Show/change IP routing table.
routed A daemon, invoked at boot time, to manage internet routing tables.
rpcgen An RPC protocol compiler. Parse a file written in the RPC language.
rpcinfo Shows RPC information. Makes an RPC call to an RPC server and reports the findings.
rpm A package manager for linux distributions. Originally developed for RedHat Linux.
rsh Remote shell. Connects to a specified host and executes commands.
rshd A daemon that acts as a server for rsh and rcp commands.
rsync A versitile to for copying files remotely and locally.
runlevel Shows previous and current SysV runlevel.
rup Remote status display. Shows current system status for all or specified hosts on the local network.
ruptime Shows uptime and login details of the machines on the local network.
rusers Shows the list of the users logged-in to the host or on all machines on the local network.
rusersd The rsuerd daemon acts as a server that responds to the queries from rsuers command.
rwall Sends messages to all users on the local network.
rwho Reports who is logged-in to the hosts on the local network.
rwhod Acts as a server for rwho and ruptime commands.
Linux Commands – S
Command Description
sane-find-scanner Find SCSI and USB scanner and determine their device files.
scanadf Retrieve multiple images from a scanner equipped with an automatic document feeder (ADF).
scanimage Read images from image aquistion devices (scanner or camera) and display on standard output in PNM (Portable aNyMap) format.
scp Copy files between hosts on a network securely using SSH.
screen A window manager that enables multiple pseudo-terminals with the help of ANSI/VT100 terminal emulation.
script Used to make a typescript of everything displayed on the screen during a terminal session.
sdiff Shows two files side-by-side and highlights the differences.
sed Stream editor for filtering and transforming text (from a file or a pipe input).
select Synchronous I/O multiplexing.
sendmail It’s a mail router or an MTA (Mail Transfer Agent). sendmail support can send a mail to one or more recepients using necessary protocols.
sensors Shows the current readings of all sensor chips.
seq Displays an incremental sequence of numbers from first to last.
set Used to manipulate shell variables and functions.
setfdprm Sets floppy disk parameters as provided by the user.
setkeycodes Load kernel scancode-to-keycode mapping table entries.
setleds Show/change LED light settings of the keyboard.
setmetamode Define keyboard meta key handling. Without arguments, shows current meta key mode.
setquota Set disk quotas for users and groups.
setsid Run a program in a new session.
setterm Set terminal attributes.
sftp Secure File Transfer program.
sh Command interpreter (shell) utility.
sha1sum Compute and check 160-bit SHA1 checksum to verify file integrity.
shift Shift positional parameters.
shopt Shell options.
showkey Examines codes sent by the keyboard displays them in printable form.
showmount Shows information about NFS server mount on the host.
shred Overwrite a file to hide its content (optionally delete it), making it harder to recover it.
shutdown Power-off the machine.
size Lists section size and the total size of a specified file.
skill Send a signal to processes.
slabtop Show kernel slab cache information in real-time.
slattach Attack a network interface to a serial line.
sleep Suspend execution for a specified amount of time (in seconds).
slocate Display matches by searching filename databases. Takes ownership and file permission into consideration.
snice Reset priority for processes.
sort Sort lines of text files.
source Run commands from a specified file.
split Split a file into pieces of fixed size.
ss Display socket statistics, similar to netstat.
ssh An SSH client for logging in to a remote machine. It provides encrypted communication between the hosts.
ssh-add Adds private key identities to the authentication agent.
ssh-agent It holds private keys used for public key authentication.
ssh-keygen It generates, manages, converts authentication keys for ssh.
ssh-keyscan Gather ssh public keys.
sshd Server for the ssh program.
stat Display file or filesystem status.
statd A daemon that listens for reboot notifications from other hosts, and manages the list of hosts to be notified when the local system reboots.
strace Trace system calls and signals.
strfile Create a random access file for storing strings.
strings Search a specified file and prints any printable strings with at least four characters and followed by an unprintable character.
strip Discard symbols from object files.
stty Change and print terminal line settings.
su Change user ID or become superuser.
sudo Execute a command as superuser.
sum Checksum and count the block in a file.
suspend Suspend the execution of the current shell.
swapoff Disable devices for paging and swapping.
swapon Enable devices for paging and swapping.
symlink Create a symbolic link to a file.
sync Synchronize cached writes to persistent storage.
sysctl Configure kernel parameters at runtime.
sysklogd Linux system logging utilities. Provides syslogd and klogd functionalities.
syslogd Read and log system messages to the system console and log files.
Linux Commands – T
Command Description
tac Concatenate and print files in reverse order. Opposite of cat command.
tail Show the last 10 lines of each specified file(s).
tailf Follow the growth of a log file. (Deprecated command)
talk A two-way screen-oriented communication utility that allows two user to exchange messages simulateneously.
talkd A remote user communication server for talk.
tar GNU version of the tar archiving utility. Used to store and extract multiple files from a single archive.
taskset Set/retrieve a process’s CPU affinity.
tcpd Access control utility for internet services.
tcpdump Dump traffic on network. Displays a description of the contents of packets on a network interface that match the boolean expression.
tcpslice Extract pieces of tcpdump files or merge them.
tee Read from standard input and write to standard output and files.
telinit Change SysV runlevel.
telnet Telnet protocol user interface. Used to interact with another host using telnet.
telnetd A server for the telnet protocol.
test Check file type and compare values.
tftp User interface to the internet TFTP (Trivial File Transfer Protocol).
tftpd TFTP server.
time Run programs and summarize system resource usage.
timeout Execute a command with a time limit.
times Shows accumulated user and system times for the shell and it’s child processes.
tload Shows a graph of the current system load average to the specified tty.
tmpwatch Recursively remove files and directories which haven’t been accessed for the specified period of time.
top Displays real-time view of processes running on the system.
touch Change file access and modification times.
tput Modify terminal-dependent capabilities, color, etc.
tr Translate, squeeze, or delete characters from standard input and display on standard output.
tracepath Traces path to a network host discovering MTU (Maximum Transmission Unit) along this path.
traceroute Traces the route taken by the packets to reach the network host.
trap Trap function responds to hardware signals. It defines and creates handlers to run when the shell receives signals.
troff The troff processor of the groff text formatting system.
TRUE Exit with a status code indicating success.
tset Initialize terminal.
tsort Perform topological sort.
tty Display the filename of the terminal connected to standard input.
tune2fs Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems.
tunelp Set various parameters for the line printer devices.
type Write a description for a command type.
Linux Commands – U
Command Description
ul Underline text.
ulimit Get and set user limits for the calling process.
umask Set file mode creation mask.
umount Unmount specified file systems.
unalias Remove alias definitions for specified alias names.
uname Show system information.
uncompress Uncompress the files compressed with the compress command.
unexpand Convert spaces to tabs for a specified file.
unicodestart Put keyboard and console in Unicode mode.
unicodestop Revert keyboard and console from Unicode mode.
uniq Report or omit repeating lines.
units Convert units from one scalar to another.
unrar Extract files from a RAR archive.
unset Remove variable or function names.
unshar Unpack shell archive scripts.
until Execute command until a given condition is true.
uptime Tell how long the system has been running.
useradd Create a new user or update default user information.
userdel Delete a user account and related files.
usermod Modify a user account.
users Show the list of active users on the machine.
usleep Suspend execution for microsecond intervals.
uudecode Decode a binary file.
uuencode Encode a binary file.
uuidgen Created a new UUID (Universally Unique Identifier) table.
Linux Commands – V
Command Description
vdir Same as ls -l -b. Verbosely list directory contents.
vi A text editor utility.
vidmode Set the video mode for a kernel image. Displays current mode value without arguments. Alternative: rdev -v
vim Vi Improved, a text-based editor which is a successor to vi.
vmstat Shows information about processes, memory, paging, block IO, traps, disks, and CPU activity.
volname Returns volume name for a device formatted with an ISO-9660 filesystem. For example, CD-ROM.
Linux Commands – W
Command Description
w Show who is logged-on and what they’re doing.
wait Waits for a specified process ID(s) to terminate and returns the termination status.
wall Display a message on the terminals all the users who are currently logged-in.
warnquota Send mail to the users who’ve exceeded their disk quota soft limit.
watch Runs commands repeatedly until interrupted and shows their output and errors.
wc Print newline, word, and byte count for each of the specified files.
wget A non-interactive file download utility.
whatis Display one line manual page descriptions.
whereis Locate the binary, source, and man page files for a command.
which For a given command, lists the pathnames for the files which would be executed when the command runs.
while Conditionally execute commands (while loop).
who Shows who is logged on.
whoami Displays the username tied to the current effective user ID.
whois Looks for an object in a WHOIS database
write Display a message on other user’s terminal.
Linux Commands – X
Command Description
xargs Runs a command using initial arguments and then reads remaining arguments from standard input.
xdg-open Used to open a file or URL in an application preferred by the user.
xinetd Extended internet services daemon. Works similar to inetd.
xz Compress/ Decompress .xz and .lzma files.
Linux Commands – Y
Command Description
yacc Yet Another Compiler Compiler, a GNU Project parser generator.
yes Repeatedly output a line with a specified string(s) until killed.
ypbind A daemon that helps client processes to connect to an NIS server.
ypcat Shows the NIS map (or database) for the specified MapName parameter.
ypinit Sets up NIS maps on an NIS server.
ypmatch Shows values for specified keys from an NIS map.
yppasswd Change NIS login password.
yppasswdd Acts as a server for the yppasswd command. Receives and executes requests.
yppoll Shows the ID number or version of NIS map currently used on the NIS server.
yppush Forces slave NIS servers to copy updated NIS maps.
ypserv A daemon activated at system startup. It looks for information in local NIS maps.
ypset Point a client (running ypbind) to a specifc server (running ypserv).
yptest Calls various functions to check the configuration of NIS services.
ypwhich Shows the hostname for NIS server or master server for a given map.
ypxfr Transfers NIS server map from server to a local host.
Linux Commands – Z
Command Description
zcat Used to compress/uncompress files. Similar to gzip
zcmp Compare compressed files.
zdiff Compare compressed files line by line.
zdump Displays time for the timezone mentioned.
zforce Adds .gz extension to all gzipped files.
zgrep Performs grep on compressed files.
zic Creates time conversion information files using the specified input files.
zip A file compression and packaging utility.
zless Displays information of a compressed file (using less command) on the terminal one screen at a time.
zmore Displays output of a compressed file (using more command) on the terminal one page at a time.
znew Recompress .z files to .gz. files.