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LinuxBash Shell

Ultimate list of Linux bash commands

Bash is the Unix command-line interface (CLI). You'll also see it called the terminal, the command line, or the shell. It's a command language that allows us to work with files on our computers in a way that's far more efficient and powerful than using a GUI (graphical user interface)

A to Z command list 📚

Note
Use Ctrl+f to search in browsers🔎

Table

ABCDEFGHIJKLMNOPQRSTUVWXYZ

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.
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
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).

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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.

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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 directory.
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.

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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 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.

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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.

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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.

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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.

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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.

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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.

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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.

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴛᴏᴩ

K

Command Description
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.

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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.

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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.

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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.

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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).

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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 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

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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.

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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.

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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.

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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.

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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.
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.

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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.

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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.

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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.

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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.

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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.

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Quick cheat sheet 📝

Note
Examples like -a|--all option flags means, single - used for short option(-a) or| double -- used for long option(--all). Both was added for educational purpose.

Contents

Command Information

man chmod                   # Display page manual of a command
man -f|--whatis chmod       # Display short description about a command
man -k|--apropos permission # Display all related commands from a specific keyword

chmod --help                # Display usage options of a command

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Command History

history                                # View all previous commands
history | grep foo                     # View the commands using a specific word
history | grep -E|--extended-regexp -i|--ignore-case 'foo1|foo2|foo3' # View the commands using more than 1 specific word(case sensitive)
history | head -n|--lines 3            # View the first 3 executed commands
history 3                              # View the last 3 executed commands
history -d 99                          # Clear a command from a specific line 
history -c                             # Clears all history commands
!!                                     # Run the last command executed

touch foo.sh                           # <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<┐
chmod +x !$                            # !$ is the last argument of the last command i.e. foo.sh <<<<┘

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Navigating Directories

pwd                       # Print current directory path
ls                        # List directories
ls -a|--all               # List directories including hidden
ls -l                     # List directories in long form
ls -l -h|--human-readable # List directories in long form with human readable sizes
ls -t                     # List directories by modification time, newest first
stat foo.txt              # List size, created and modified timestamps for a file
stat foo                  # List size, created and modified timestamps for a directory
tree                      # List directory and file tree
tree -a                   # List directory and file tree including hidden
tree -d                   # List directory tree
cd foo                    # Go to foo sub-directory
cd                        # Go to home directory
cd ~                      # Go to home directory
cd -                      # Go to last directory
pushd foo                 # Go to foo sub-directory and add previous directory to stack
popd                      # Go back to directory in stack saved by `pushd`

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Creating Directories

mkdir foo                        # Create a directory
mkdir foo bar                    # Create multiple directories
mkdir -p|--parents foo/bar       # Create nested directory
mkdir -p|--parents {foo,bar}/baz # Create multiple nested directories

mktemp -d|--directory            # Create a temporary directory

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Moving Directories

cp -R|--recursive foo bar                              # Copy directory
mv foo bar                                             # Move directory

rsync -z|--compress -v|--verbose /foo /bar             # Copy directory, overwrites destination
rsync --ignore-existing -a|--archive-a|--archive -z|--compress -v|--verbose /foo /bar # Copy directory, without overwriting destination
rsync -avz /foo username@hostname:/bar                 # Copy local directory to remote directory
rsync -avz username@hostname:/foo /bar                 # Copy remote directory to local directory

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Deleting Directories

rmdir foo                        # Delete non-empty directory
rm -r|--recursive foo            # Delete directory including contents
rm -r|--recursive -f|--force foo # Delete directory including contents, ignore nonexistent files and never prompt

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Creating Files

touch foo.txt          # Create file or update existing files modified timestamp
touch foo.txt bar.txt  # Create multiple files
touch {foo,bar}.txt    # Create multiple files
touch test{1..3}       # Create test1, test2 and test3 files
touch test{a..c}       # Create testa, testb and testc files

mktemp                 # Create a temporary file

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Standard Output, Standard Error and Standard Input

echo "foo" > bar.txt       # Overwrite file with content
echo "foo" >> bar.txt      # Append to file with content

ls exists 1> stdout.txt    # Redirect the standard output to a file
ls noexist 2> stderror.txt # Redirect the standard error output to a file
ls > out.txt 2>&1          # Redirect standard output and error to a file
ls > /dev/null             # Discard standard output and error

read foo                   # Read from standard input and write to the variable foo

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Moving Files

cp foo.txt bar.txt                                 # Copy file
mv foo.txt bar.txt                                 # Move file

rsync -z|--compress -v|--verbose /foo.txt /bar     # Copy file quickly if not changed
rsync -z|--compress -v|--verbose /foo.txt /bar.txt # Copy and rename file quickly if not changed

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Deleting Files

rm foo.txt            # Delete file
rm -f|--force foo.txt # Delete file, ignore nonexistent files and never prompt

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Reading Files

cat foo.txt            # Print all contents
less foo.txt           # Print some contents at a time (g - go to top of file, SHIFT+g, go to bottom of file, /foo to search for 'foo')
head foo.txt           # Print top 10 lines of file
tail foo.txt           # Print bottom 10 lines of file
open foo.txt           # Open file in the default editor
wc foo.txt             # List number of lines words and characters in the file

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File Permissions

# Permission rwx Binary
7 read, write and execute rwx 111
6 read and write rw- 110
5 read and execute r-x 101
4 read only r-- 100
3 write and execute -wx 011
2 write only -w- 010
1 execute only --x 001
0 none --- 000

For a directory, execute means you can enter a directory.

User Group Others Description
6 4 4 User can read and write, everyone else can read (Default file permissions)
7 5 5 User can read, write and execute, everyone else can read and execute (Default directory permissions)
  • u - User
  • g - Group
  • o - Others
  • a - All of the above
ls -l /foo.sh            # List file permissions
chmod +100 foo.sh        # Add 1 to the user permission
chmod -100 foo.sh        # Subtract 1 from the user permission
chmod u+x foo.sh         # Give the user execute permission
chmod g+x foo.sh         # Give the group execute permission
chmod u-x,g-x foo.sh     # Take away the user and group execute permission
chmod u+x,g+x,o+x foo.sh # Give everybody execute permission
chmod a+x foo.sh         # Give everybody execute permission
chmod +x foo.sh          # Give everybody execute permission

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Finding Files

Find binary files for a command.

type -a wget                              # Display all locations of executable
which -a wget                             # Display all locations of executables 
whereis wget                              # Find the binary, source, and manual page files

locate uses an index and is fast.

updatedb                                   # Update the index

locate foo.txt                             # Find a file
locate --ignore-case                       # Find a file and ignore case
locate f*.txt                              # Find a text file starting with 'f'

find doesn't use an index and is slow.

find /path -name foo.txt                   # Find a file
find /path -iname foo.txt                  # Find a file with case insensitive search
find /path -name "*.txt"                   # Find all text files
find /path -name foo.txt -delete           # Find a file and delete it
find /path -name "*.png" -exec pngquant {} # Find all .png files and execute pngquant on it
find /path -type f -name foo.txt           # Find a file
find /path -type d -name foo               # Find a directory
find /path -type l -name foo.txt           # Find a symbolic link
find /path -type f -mtime +30              # Find files that haven't been modified in 30 days
find /path -type f -mtime +30 -delete      # Delete files that haven't been modified in 30 days

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Find in Files

grep 'foo' /bar.txt                         # Search for 'foo' in file 'bar.txt'
grep 'foo' /bar -r|--recursive              # Search for 'foo' in directory 'bar'
grep 'foo' /bar -R|--dereference-recursive  # Search for 'foo' in directory 'bar' and follow symbolic links
grep 'foo' /bar -l|--files-with-matches     # Show only files that match
grep 'foo' /bar -L|--files-without-match    # Show only files that don't match
grep 'Foo' /bar -i|--ignore-case            # Case insensitive search
grep 'foo' /bar -x|--line-regexp            # Match the entire line
grep 'foo' /bar -C|--context 1              # Add N line of context above and below each search result
grep 'foo' /bar -v|--invert-match           # Show only lines that don't match
grep 'foo' /bar -c|--count                  # Count the number lines that match
grep 'foo' /bar -n|--line-number            # Add line numbers
grep 'foo' /bar --colour                    # Add colour to output
grep 'foo\|bar' /baz -R                     # Search for 'foo' or 'bar' in directory 'baz'
grep --extended-regexp|-E 'foo|bar' /baz -R # Use regular expressions
grep -E 'foo|bar' /baz -R                   # Use regular expressions

Replace in Files

sed 's/fox/bear/g' foo.txt               # Replace fox with bear in foo.txt and output to console
sed 's/fox/bear/gi' foo.txt              # Replace fox (case insensitive) with bear in foo.txt and output to console
sed 's/red fox/blue bear/g' foo.txt      # Replace red with blue and fox with bear in foo.txt and output to console
sed 's/fox/bear/g' foo.txt > bar.txt     # Replace fox with bear in foo.txt and save in bar.txt
sed 's/fox/bear/g' foo.txt -i|--in-place # Replace fox with bear and overwrite foo.txt

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Symbolic Links

ln -s|--symbolic foo bar            # Create a link 'bar' to the 'foo' folder
ln -s|--symbolic -f|--force foo bar # Overwrite an existing symbolic link 'bar'
ls -l                               # Show where symbolic links are pointing

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Compressing Files

zip

Compresses one or more files into *.zip files.

zip foo.zip /bar.txt                # Compress bar.txt into foo.zip
zip foo.zip /bar.txt /baz.txt       # Compress bar.txt and baz.txt into foo.zip
zip foo.zip /{bar,baz}.txt          # Compress bar.txt and baz.txt into foo.zip
zip -r|--recurse-paths foo.zip /bar # Compress directory bar into foo.zip

gzip

Compresses a single file into *.gz files.

gzip /bar.txt foo.gz           # Compress bar.txt into foo.gz and then delete bar.txt
gzip -k|--keep /bar.txt foo.gz # Compress bar.txt into foo.gz

tar -c

Compresses (optionally) and combines one or more files into a single *.tar, *.tar.gz, *.tpz or *.tgz file.

tar -c|--create -z|--gzip -f|--file=foo.tgz /bar.txt /baz.txt # Compress bar.txt and baz.txt into foo.tgz
tar -c|--create -z|--gzip -f|--file=foo.tgz /{bar,baz}.txt    # Compress bar.txt and baz.txt into foo.tgz
tar -c|--create -z|--gzip -f|--file=foo.tgz /bar              # Compress directory bar into foo.tgz

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Decompressing Files

unzip

unzip foo.zip          # Unzip foo.zip into current directory

gunzip

gunzip foo.gz           # Unzip foo.gz into current directory and delete foo.gz
gunzip -k|--keep foo.gz # Unzip foo.gz into current directory

tar -x

tar -x|--extract -z|--gzip -f|--file=foo.tar.gz # Un-compress foo.tar.gz into current directory
tar -x|--extract -f|--file=foo.tar              # Un-combine foo.tar into current directory

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Packages

apt update                          # Refreshes repository index
apt search wget                     # Search for a package
apt show wget                       # List information about the wget package
apt list --all-versions wget        # List all versions of the package
apt install wget                    # Install the latest version of the wget package
apt install wget=1.2.3              # Install a specific version of the wget package
apt remove wget                     # Removes the wget package
apt upgrade                         # Upgrades all upgradable packages
apt clean                           # Clears out the local repository of downloaded package files

dpkg -i|--install package_name.deb  # Install deb file
rpm -i|--install package_name.rpm   # Install rpm file 

Install package source code

tar zxvf sourcecode.tar.gz
cd sourcecode
./configure
make
make install

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Disk Usage

df                     # List disks, size, used and available space
df -h|--human-readable # List disks, size, used and available space in a human readable format

du                     # List current directory, subdirectories and file sizes
du /foo/bar            # List specified directory, subdirectories and file sizes
du -h|--human-readable # List current directory, subdirectories and file sizes in a human readable format
du -d|--max-depth      # List current directory, subdirectories and file sizes within the max depth
du -d 0                # List current directory size

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Memory Usage

free                   # Show memory usage
free -h|--human        # Show human readable memory usage
free -h|--human --si   # Show human readable memory usage in power of 1000 instead of 1024
free -s|--seconds 5    # Show memory usage and update continuously every five seconds

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Shutdown and Reboot

shutdown                     # Shutdown in 1 minute
shutdown now                 # Immediately shut down
shutdown +5                  # Shutdown in 5 minutes

shutdown -r|--reboot         # Reboot in 1 minute
shutdown -r|--reboot now     # Immediately reboot
shutdown -r|--reboot +5      # Reboot in 5 minutes
shutdown -c                  # Cancel a shutdown or reboot

reboot                       # Reboot now
reboot -f                    # Force a reboot

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Identifying Processes

top                    # List all processes interactively
htop                   # List all processes interactively
ps ax                  # List all processes
pidof foo              # Return the PID of all foo processes

CTRL+Z                 # Suspend a process running in the foreground
bg                     # Resume a suspended process and run in the background
fg                     # Bring the last background process to the foreground
fg 1                   # Bring the background process with the PID to the foreground

sleep 30 &             # Sleep for 30 seconds and move the process into the background
jobs                   # List all background jobs
jobs -p                # List all background jobs with their PID

lsof                   # List all open files and the process using them
lsof -itcp:4000        # Return the process listening on port 4000

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Process Priority

Process priorities go from -20 (highest) to 19 (lowest).

nice -n -20 foo        # Change process priority by name
renice 20 PID          # Change process priority by PID
ps -o ni PID           # Return the process priority of PID

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Killing Processes

CTRL+C                 # Kill a process running in the foreground
kill PID               # Shut down process by PID gracefully. Sends TERM signal.
kill -9 PID            # Force shut down of process by PID. Sends SIGKILL signal.
pkill foo              # Shut down process by name gracefully. Sends TERM signal.
pkill -9 foo           # force shut down process by name. Sends SIGKILL signal.
killall foo            # Kill all process with the specified name gracefully.

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Date & Time

date                            # Print the date and time
date --iso-8601                 # Print the ISO8601 date
date --iso-8601=ns              # Print the ISO8601 date and time

date -s "02 DEC 2020 12:02:02"  # Manually change date and time
dpkg-reconfigure tzdata         # Change date/timezone

uptime                          # Print how long the system has been running
time tree                       # Print amount of time to tree takes to execute

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Scheduled Tasks

   *      *         *         *           *
Minute, Hour, Day of month, Month, Day of the week
crontab -l                 # List cron tab
crontab -e                 # Edit cron tab in Vim
crontab /path/crontab      # Load cron tab from a file
crontab -l > /path/crontab # Save cron tab to a file

* * * * * foo              # Run foo every minute
*/15 * * * * foo           # Run foo every 15 minutes
0 * * * * foo              # Run foo every hour
15 6 * * * foo             # Run foo daily at 6:15 AM
44 4 * * 5 foo             # Run foo every Friday at 4:44 AM
0 0 1 * * foo              # Run foo at midnight on the first of the month
0 0 1 1 * foo              # Run foo at midnight on the first of the year

at -l                      # List scheduled tasks
at -c 1                    # Show task with ID 1
at -r 1                    # Remove task with ID 1
at now + 2 minutes         # Create a task in Vim to execute in 2 minutes
at 12:34 PM next month     # Create a task in Vim to execute at 12:34 PM next month
at tomorrow                # Create a task in Vim to execute tomorrow

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

User Management

adduser username                                   # To add a new user
passwd -l|--lock username                          # To change the password of a user
userdel username                                   # To remove user
userdel -r|--remove username                       # To remove user with home directory and mail spool
usermod -a|--append -G|--groups GROUPNAME USERNAME # To add a user to a group
deluser USER GROUPNAME                             # To remove a user from a group

last                                               # Shows information of all the users logged in
last username                                      # Gives information of a particular user

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

HTTP Requests

curl https://example.com                               # Return response body
curl -i|--include https://example.com                  # Include status code and HTTP headers
curl -L|--location https://example.com                 # Follow redirects
curl -O|--remote-name foo.txt https://example.com      # Output to a text file
curl -H|--header "User-Agent: Foo" https://example.com # Add a HTTP header
curl -X|--request POST -H "Content-Type: application/json" -d|--data '{"foo":"bar"}' https://example.com # POST JSON
curl -X POST -H --data-urlencode foo="bar" http://example.com  # POST URL Form Encoded

wget https://example.com/file.txt                              # Download a file to the current directory
wget -O|--output-document foo.txt https://example.com/file.txt # Output to a file with the specified name

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Network Troubleshooting

ping example.com            # Send multiple ping requests using the ICMP protocol
ping -c 10 -i 5 example.com # Make 10 attempts, 5 seconds apart

ip addr                     # List IP addresses on the system
ip route show               # Show IP addresses to router

curl ifconfig.me            # Obtain external IP address

netstat -i|--interfaces     # List all network interfaces and in/out usage
netstat -l|--listening      # List all open ports

traceroute example.com      # List all servers the network traffic goes through

mtr -w|--report-wide example.com                                    # Continually list all servers the network traffic goes through
mtr -r|--report -w|--report-wide -c|--report-cycles 100 example.com # Output a report that lists network traffic 100 times

nmap 0.0.0.0                # Scan for the 1000 most common open ports on localhost
nmap 0.0.0.0 -p1-65535      # Scan for open ports on localhost between 1 and 65535
nmap 192.168.4.3            # Scan for the 1000 most common open ports on a remote IP address
nmap -sP 192.168.1.1/24     # Discover all machines on the network by ping'ing them

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

DNS

dig example.com                 # Show query information of domain A records
dig -4 example.com              # Show IPv4 A records
dig -6 example.com              # Show IPv6 AAA records
dig example.com @nameserver     # Show query of a specific nameserver
dig example.com -p 123          # Show query of a specific port number

cat /etc/resolv.conf            # Nameservers file
cat /etc/systemd/resolved.conf  # DNS resolver config file

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Hardware

lsusb                  # List USB devices
lspci                  # List PCI hardware
lshw                   # List all hardware

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

System Information

uname -s               # Print kernel name
uname -r               # Print kernel release
uname -m               # Print Architecture
uname -o               # Print Operating System

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Terminal Multiplexers

Start multiple terminal sessions. Active sessions persist reboots. tmux is more modern than screen.

tmux             # Start a new session (CTRL-b + d to detach)
tmux ls          # List all sessions
tmux attach -t 0 # Reattach to a session

screen           # Start a new session (CTRL-a + d to detach)
screen -ls       # List all sessions
screen -R 31166  # Reattach to a session

exit             # Exit a session

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Secure Shell Protocol (SSH)

ssh hostname                 # Connect to hostname using your current user name over the default SSH port 22
ssh -i foo.pem hostname      # Connect to hostname using the identity file
ssh user@hostname            # Connect to hostname using the user over the default SSH port 22
ssh user@hostname -p 8765    # Connect to hostname using the user over a custom port
ssh ssh://user@hostname:8765 # Connect to hostname using the user over a custom port

Set default user and port in ~/.ssh/config, so you can just enter the name next time:

$ cat ~/.ssh/config
Host name
  User foo
  Hostname 127.0.0.1
  Port 8765
$ ssh name

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Secure Copy

scp foo.txt ubuntu@hostname:/home/ubuntu                    # Copy foo.txt into the specified remote directory
scp ubuntu@hostname:/home/ubuntu/foo.txt /C:\Users\Admin    # Copy foo.txt from the specified remote directory

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Bash Profile

  • bash - .bashrc
  • zsh - .zshrc
# Always run ls after cd
function cd {
  builtin cd "$@" && ls
}

# Prompt user before overwriting any files
alias cp='cp --interactive'
alias mv='mv --interactive'
alias rm='rm --interactive'

# Always show disk usage in a human readable format
alias df='df -h'
alias du='du -h'

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Bash Script

Variables

#!/bin/bash

foo=123                # Initialize variable foo with 123
declare -i foo=123     # Initialize an integer foo with 123
declare -r foo=123     # Initialize readonly variable foo with 123
echo $foo              # Print variable foo
echo ${foo}_'bar'      # Print variable foo followed by _bar
echo ${foo:-'default'} # Print variable foo if it exists otherwise print default

export foo             # Make foo available to child processes
unset foo              # Make foo unavailable to child processes and current session

Environment Variables

#!/bin/bash

set            # List all environment variables
echo $PATH     # Print PATH environment variable
export FOO=Bar # Set an environment variable

Functions

#!/bin/bash

greet() {
  local world="World"
  echo "$1 $world"
  return "$1 $world"
}
greet "Hello"
greeting=$(greet "Hello")

Exit Codes

#!/bin/bash

exit 0   # Exit the script successfully
exit 1   # Exit the script unsuccessfully
echo $?  # Print the last exit code

Conditional Statements

Boolean Operators

  • $foo - Is true
  • !$foo - Is false

Numeric Operators

  • -eq - Equals
  • -ne - Not equals
  • -gt - Greater than
  • -ge - Greater than or equal to
  • -lt - Less than
  • -le - Less than or equal to
  • -e foo.txt - Check file exists
  • -z foo - Check if variable exists

String Operators

  • = - Equals
  • == - Equals
  • -z - Is null
  • -n - Is not null
  • < - Is less than in ASCII alphabetical order
  • > - Is greater than in ASCII alphabetical order

If Statements

#!/bin/bash

[[
if [[$foo = 'bar']]; then
  echo 'one'
elif [[$foo = 'bar']] || [[$foo = 'baz']]; then
  echo 'two'
elif [[$foo = 'ban']] && [[$USER = 'bat']]; then
  echo 'three'
else
  echo 'four'
fi
]]

Inline If Statements

#!/bin/bash

[[ $USER = 'rehan' ]] && echo 'yes' || echo 'no'

While Loops

#!/bin/bash

[
declare -i counter
counter=10
while [$counter -gt 2]; do
  echo The counter is $counter
  counter=counter-1
done
]

For Loops

#!/bin/bash

for i in {0..10..2}
  do
    echo "Index: $i"
  done

for filename in file1 file2 file3
  do
    echo "Content: " >> $filename
  done

for filename in *;
  do
    echo "Content: " >> $filename
  done

Case Statements

#!/bin/bash

echo "What's the weather like tomorrow?"
read weather

case $weather in
  sunny | warm ) echo "Nice weather: " $weather
  ;;
  cloudy | cool ) echo "Not bad weather: " $weather
  ;;
  rainy | cold ) echo "Terrible weather: " $weather
  ;;
  * ) echo "Don't understand"
  ;;
esac

⬆ ʀᴇᴛᴜʀɴ ᴛᴏ ᴄᴏɴᴛᴇɴᴛꜱ

Special characters 🔣

Char. Description
~  Home directory [tilde]. The current user's home directory location
/  Filename path separator [forward slash]. Separates the components of a filename
\  Escape [backslash]. A quoting mechanism for single characters. \X escapes the character X. It preserves the literal value of the next character that follows, with the exception of newline
 Pipe. It passes the output (stdout) of a previous command to the input (stdin) of the next one, or to the shell. This is a method of chaining commands together
||  OR logical operator causes a return of 0 (success) if either of the linked test conditions is true
&&  AND logical operator causes a return of 0 (success) only if both the linked test conditions are true
-  Option flag for a command or filter. The default parameter in parameter substitution
--  The double-dash prefixes is the long (verbatim) option flags for commands
>, >>, <  Redirect a command's output or input into a file
>|  Force redirection (even if the noclobber option is set). This will forcibly overwrite an existing file
&  Run job in background. A command followed by an & will run in the background
"  Partial quoting [double quote]. "STRING" preserves (from interpretation) most of the special characters within STRING
'  Full quoting [single quote]. 'STRING' preserves all special characters within STRING. This is a stronger form of quoting than "STRING"
' '  Single quotes. Protect the text inside them so that it has a literal meaning
""  Double quotes protect the text inside them from being split into multiple words or arguments, yet allow substitutions to occur, meaning most other special characters is usually prevented
" "  Whitespace. This is a tab, newline, vertical tab, form feed, carriage return, or space. Bash uses whitespace to determine where words begin and end
;  Command separator [semicolon]. Used to separate multiple commands that are on the same line
:  Null command [colon]. This is the shell equivalent of a "NOP" (no op, a do-nothing operation). It may be considered a synonym for the shell builtin true
!  Reverse (or negate) [exclamation]. The ! operator inverts the exit status of the command to which it is applied. It also inverts the meaning of a test operator
*  Wild card [asterisk]. Glob, "wildcard" characters which match parts of filenames (e.g. ls *.txt)
{ }  Inline group [curly brackets]. Commands inside the curly braces are treated as if they were one command. It is convenient to use these when Bash syntax requires only one command and a function doesn't feel warranted
( )  Subshell group [bracket].Commands within are executed in a subshell (a new process) Used much like a sandbox, if a command causes side effects (like changing variables), it will have no effect on the current shell
[ ]  Test expression between [ ]. Is part of the shell builtin test
[[ ]]  Test expression between [[ ]]. More flexible than the single-bracket [ ] test
(( ))  Integer expansion. Expand and evaluate integer expression between (( ))
;;  Terminator in a case option [double semicolon]
;;&, ;&  Terminators in a case option
,, ,  Lowercase conversion in parameter substitution
?  Test operator[question mark]. Within certain expressions, the ? indicates a test for a condition
#  Comment [number sign]. Lines in files beginning with a # (with the exception of #!) are comments and will not be executed

Keyboard control ⌨️

Key Function
Ctrl+a Moves cursor to beginning of text in line
Ctrl+e Moves cursor to end of text in line
Ctrl+b Moves cursor backward one character position
Ctrl+f Moves cursor forward one character position
Ctrl+p Fetch previous command from history buffer
Ctrl+n Fetch next command from history buffer
Ctrl+r Reverse search commands in history buffer
Ctrl+u Erase a line of input from cursor right to left of line
Ctrl+k Erase a line of input from cursor left to right of line
Ctrl+y Fetch back command previously erased
Ctrl+t Reverses the position of the character the cursor is on with the previous character
Ctrl+z Pauses a foreground job
Ctrl+c Break/Terminate a foreground job
Ctrl+o Accept the current line for execution and fetch the next command
Ctrl+l Clear screen
Ctrl+s Suspend
Ctrl+q Resume
Ctrl+d Log out from a shell (similar to exit)


Online Cheat Sheet :feelsgood: for quick references of commands and codes

cheat.sh
image
Terminal:

curl cht.sh/keyword
# or
curl cheat.sh/keyword

Browser:

https://cht.sh/keyword
https://cheat.sh/keyword

Install cheat script manually for offline usage

# Install for all users:
curl -s https://cht.sh/:cht.sh | sudo tee /usr/local/bin/cht.sh && sudo chmod +x /usr/local/bin/cht.sh

# Run script:
cht.sh

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