atoz

#!/bin/sh
set -euf

echo "A list of commands from A to Z:

A
accept         Accept or Reject CUPS 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.
acpi_available 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 or show existing ones.
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.
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             Schedule command execution at a given time, reading commands from a 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 write to stdout.
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).

B
badblocks Search a disk partition for bad sectors.
banner    Print characters as a poster.
basename  Display filenames with directoy or suffix.
bash      GNU Bourne-Again Shell.
batch     Run commands entered from stdin.
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      Attach a name to a socket.
bison     A GNU parser generator, compatible with yacc.
break     Exit from a loop (eg: for, while, select).
builtin   Run shell builtin commands, make custom functions for commands extending their functionality.
bzcmp     Call the cmp program for bzip2 compressed files.
bzdiff    Call the diff program for bzip2 compressed files.
bzgrep    Call grep for bzip2 compressed files.
bzip2     A block-sorting file compressor used to shrink given files.
bzless    Apply ‘less’ (show info one page at a time) to bzip2 compressed files.
bzmore    Apply ‘more’ (an inferior version of less) to bzip2 compressed files.

C
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.

D
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 LS_COLORS 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.

E
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.

F
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.

G
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.

H
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.

I
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.

J
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.

K
kbd_mode	 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.

L
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.

M
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.

N
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.

O
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).

P
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 ECHO_REQUEST 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

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.

R
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.

S
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.

T
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.

U
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.
unicode_start	 Put keyboard and console in Unicode mode.
unicode_stop	 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.

V
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.

W
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.

X
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.

Y
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.

Z
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.
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