Linux Commands Library

The <code>a2dismod</code> command is used to disable Apache2 modules. It removes symbolic links from the <code>/etc/apache2/mods-enabled</code> directory that were previously created by <code>a2enmod</code>. After disabling modules, Apache needs to be restarted to apply the changes.

a2dismod [OPTION]... [MODULE]...

The <code>a2dissite</code> command is used to disable Apache2 website configurations. It removes symbolic links from the <code>/etc/apache2/sites-enabled</code> directory that were previously created by <code>a2ensite</code>. After disabling sites, Apache needs to be restarted to apply the changes.

a2dissite [OPTION]... [SITE]...

The <code>a2enmod</code> command is used to enable Apache2 modules. It creates symbolic links from the <code>/etc/apache2/mods-available</code> directory to <code>/etc/apache2/mods-enabled</code>. After enabling modules, Apache needs to be restarted to apply the changes.

a2enmod [OPTION]... [MODULE]...

The <code>a2ensite</code> command is used to enable Apache2 website configurations. It creates symbolic links from the <code>/etc/apache2/sites-available</code> directory to <code>/etc/apache2/sites-enabled</code>. After enabling a site, Apache needs to be restarted to apply the changes.

a2ensite [OPTION]... [SITE]...

The <code>ab</code> (Apache Benchmark) command is a performance testing tool for HTTP servers. It shows how your Apache installation performs by generating load to the server. This tool quickly identifies how many requests per second your Apache server is capable of handling.

ab [options] [http[s]://]hostname[:port]/path

The <code>abort</code> command is used to terminate a process abnormally. It generates a core dump and can be used to diagnose program errors or forcefully stop a process that is not responding.

abort [--help] [--version]

The <code>ac</code> command prints statistics about users' connect time on a Unix system. It reads the <code>/var/log/wtmp</code> file (or the file specified with the -f option) and reports the total connect time for all users or individual users.

ac [options] [users...]

The <code>access</code> command checks whether the calling user or process has access permissions for a file or files. It returns 0 (success) if the user has the specified access rights, and non-zero (failure) otherwise.

access [-acfmrwx] [-e] [-h] file ...

The <code>aclocal</code> command is part of the GNU Autotools suite. It generates an <code>aclocal.m4</code> file by scanning <code>configure.ac</code> or <code>configure.in</code> for uses of autoconf macros and collecting the required macro definitions into a single file for use with autoconf.

aclocal [OPTION]...

The <code>add-apt-repository</code> command adds a new repository to the list of available APT package sources. It can add both standard repositories and Personal Package Archives (PPAs) to the system.

add-apt-repository [options] repository

The <code>addgroup</code> command creates a new group on the system. It is a more user-friendly alternative to the lower-level <code>groupadd</code> command, and is commonly used on Debian-based Linux distributions like Ubuntu.

addgroup [options] [--gid ID] [--system] [--group] group

The <code>adduser</code> command creates a new user account on the system with a home directory and other default settings. It is a higher-level, more user-friendly alternative to the lower-level <code>useradd</code> command.

adduser [options] [--home DIR] [--shell SHELL] [--no-create-home] [--uid ID] [--firstuid ID] [--lastuid ID] [--gecos GECOS] [--ingroup GROUP | --gid ID] [--disabled-password] [--disabled-login] [--encrypt-home] [--add_extra_groups] [--quiet] user

The <code>alias</code> command creates or lists command aliases, allowing users to create shortcuts for longer commands or to customize command behavior with predefined options.

alias [name[=value] ...]

The <code>alsamixer</code> command provides a text-based user interface for adjusting audio volume and settings using the ALSA (Advanced Linux Sound Architecture) sound system.

alsamixer [options]

The <code>amixer</code> command is a command-line mixer for ALSA (Advanced Linux Sound Architecture) sound card drivers, allowing users to control audio settings and volume from the terminal.

amixer [options] [command]

The <code>anacron</code> command runs commands periodically with a frequency specified in days, executing tasks that may have been missed while the system was powered off, unlike cron which requires the system to be running at the scheduled time.

anacron [-s] [-f] [-n] [-d] [-q] [-t anacrontab] [-S spooldir] [job...]

The <code>apropos</code> command searches the manual page names and descriptions for keywords and displays a list of matching manual pages. It's essentially equivalent to using <code>man -k</code> and is useful for finding commands related to a specific topic when you don't know the exact command name.

apropos [OPTION...] KEYWORD...

The <code>apt</code> command is a high-level package management tool for Debian and Ubuntu-based Linux distributions, providing a user-friendly interface for installing, updating, removing, and managing software packages.

apt [options] command

The <code>apt-cache</code> command is used to query the APT package cache on Debian-based systems, providing information about available packages, dependencies, versions, and package details.

apt-cache [options] command

The <code>apt-get</code> command is a powerful command-line tool for handling packages in Debian and Ubuntu-based Linux distributions, providing functionalities for installing, upgrading, configuring, and removing software packages.

apt-get [options] command

The <code>apt-key</code> command is used to manage the keys used by apt to authenticate packages. These keys are used to ensure that the packages downloaded by apt are from trusted sources.

apt-key [options] command [arguments]

The <code>apt-mark</code> command is used to mark packages as manually or automatically installed and to manipulate the dpkg selections, such as hold, unhold, install, or remove.

apt-mark [options] {auto|manual|hold|unhold|showauto|showmanual|showhold} [package...]

The <code>arch</code> command displays the machine architecture name of the current system. It is a simple command that prints the hardware name in a standard format.

arch

The <code>arecord</code> command is a command-line sound recorder and player for the ALSA (Advanced Linux Sound Architecture) sound system. It can be used to record audio from various input sources such as microphones, line-in, and capture monitors.

arecord [options] [filename]

The <code>arp</code> command manipulates or displays the kernel's IPv4 network neighbor cache. It can add entries to the table, delete entries, or display the current content of the ARP cache.

arp [-vn] [-H type] [-i if] [-a] [hostname]
arp [-v] [-i if] -d hostname [pub]
arp [-v] [-H type] [-i if] -s hostname hw_addr [temp]
arp [-v] [-H type] [-i if] -s hostname hw_addr [netmask nm] pub
arp [-v] [-H type] [-i if] -Ds hostname ifname [netmask nm] pub

The <code>arping</code> command sends ARP (Address Resolution Protocol) requests to a neighboring host or gateway and displays the responses. It is useful for network troubleshooting, checking for duplicate IP addresses, and confirming connectivity at the link layer.

arping [options] destination

The <code>as</code> command is the GNU assembler. It is used to convert assembly language code into object files that can be linked to create executable programs. It is a key component in the compilation toolchain.

as [options] -o objfile file.s

The <code>aspell</code> command is a spell checker that can be used interactively or in batch mode to check the spelling of text files. It offers suggestions for misspelled words and can be customized with different dictionaries and personal word lists.

aspell [options] <command>

The <code>at</code> command is used to schedule commands to be executed once at a later time. Unlike cron, which is used for recurring tasks, at is ideal for one-time scheduled tasks.

at [-V] [-q queue] [-f file] [-mMlv] timespec...
at [-V] [-q queue] [-f file] [-mMkv] [-t time]

The <code>atq</code> command lists the pending jobs for the at command scheduler. It displays the job number, date, hour, queue, and username for each scheduled task.

atq [-V] [-q queue] [-v]

The <code>atrm</code> command removes jobs that were previously scheduled with the <code>at</code> command. It deletes jobs from the queue of tasks to be run at a later time.

atrm [-V] job [job...]

The <code>~/.ssh/authorized_keys</code> file is a configuration file that specifies which SSH public keys are allowed to log into a user's account without a password. Each line of the file contains one public key, and the file is used by the SSH server to authenticate users via public key authentication.

Located at: ~/.ssh/authorized_keys

The <code>awk</code> command is a powerful text processing tool that treats each line of a file as a record and each word as a field. It's designed for pattern scanning and processing, making it excellent for data extraction and reporting from text files.

awk [options] 'program' file...
awk [options] -f program-file file...

The <code>basename</code> command strips directory and suffix from filenames. It is used to extract just the filename from a path or to remove a suffix from a filename.

basename NAME [SUFFIX]
basename OPTION... NAME...

The <code>bash</code> (Bourne-Again SHell) is a command processor that typically runs in a text window where the user types commands that cause actions. Bash can also read and execute commands from a file, called a shell script.

bash [options] [file [arguments]]
bash [options] -c command_string [arguments]

The <code>batch</code> command reads commands from standard input or a specified file and executes them when system load levels permit. Unlike <code>at</code>, which executes commands at a specific time, <code>batch</code> executes commands when the system load average drops below a threshold.

batch [file]

The <code>bc</code> (basic calculator) is an arbitrary precision calculator language with syntax similar to C. It allows for interactive calculations as well as programming with variables, functions, and control statements.

bc [options] [file...]
bc -l [file...]

The <code>beep</code> command generates a beep sound through the PC speaker or sound card. It's useful for providing audio notifications or alerts in scripts or terminal applications.

beep [options]

The <code>bg</code> command continues a suspended job in the background. It allows you to resume the execution of jobs that have been suspended (using Ctrl+Z) while returning control of the terminal to you.

bg [job_spec...]

The <code>blkid</code> command is a utility to locate and print block device attributes such as filesystem type, UUID, and volume label. It's commonly used for device identification and mounting filesystems.

blkid [options] [device...]

The <code>blockdev</code> command is used to call block device ioctls from the command line. It allows administrators to get or set various attributes of block devices such as hard drives, SSDs, or partitions.

blockdev [options] [commands] device

The <code>blogbench</code> command is a benchmarking tool that simulates a busy file server by performing a mix of read, write, and rewrite operations similar to a blog server, allowing you to test the I/O performance of your storage devices.

blogbench [options] -d /path/to/test/directory

The <code>bluetoothctl</code> command is an interactive command-line tool for controlling and managing Bluetooth devices on Linux systems. It provides a comprehensive set of functions for scanning, pairing, connecting, and configuring Bluetooth devices from the terminal.

bluetoothctl [command]

Ethernet bridge administration tool for Linux

brctl [OPTIONS] COMMAND [BRIDGE] [INTERFACE]

The <code>break</code> command is a shell built-in that exits from a <code>for</code>, <code>while</code>, <code>until</code>, or <code>select</code> loop. It terminates the execution of the current loop and continues with the next command after the loop.

break [n]

Manage bridge addresses and devices with the iproute2 package

bridge [OPTIONS] COMMAND

Control and manage the Btrfs filesystem in Linux

btrfs [COMMAND] [OPTIONS] <args>

Decompress files compressed with bzip2

bunzip2 [OPTIONS] [FILE...]

Decompress bzip2 files to standard output

bzcat [OPTIONS] [FILE...]

Compare bzip2 compressed files

bzcmp [cmp_options] FILE1 [FILE2]

Compare bzip2 compressed files line by line

bzdiff [OPTIONS] FILE1 [FILE2]
bzmore [OPTIONS] FILE1 [FILE2]

Search for patterns in bzip2 compressed files

bzgrep [OPTIONS] PATTERN [FILE...]
bzfgrep [OPTIONS] PATTERN [FILE...]
bzegrep [OPTIONS] PATTERN [FILE...]

The <code>bzip2</code> command compresses files using the Burrows-Wheeler block sorting text compression algorithm and Huffman coding. It generally achieves better compression than gzip but is slower.

bzip2 [options] [filenames...]
bunzip2 [options] [filenames...]

Recover data from damaged bzip2 files

bzip2recover [damaged_file.bz2]

View bzip2 compressed files using the less pager

bzless [options] file.bz2

View bzip2 compressed files using the more pager

bzmore [file.bz2 ...]

Display a calendar in the terminal

cal [options] [[[day] month] year]

The <code>cat</code> command is one of the most frequently used commands in Linux/Unix-like operating systems. <code>cat</code> stands for "concatenate" and it can read, concatenate, and write file contents to the standard output.

cat [OPTION]... [FILE]...

The <code>cd</code> command is used to change the current working directory in Linux/Unix systems. <code>cd</code> stands for "change directory" and it's one of the most essential commands for navigating the filesystem.

cd [OPTION] [DIRECTORY]

Display or manipulate a disk partition table with a curses interface

cfdisk [options] [device]

Change user password expiry information

chage [options] LOGIN

Change file attributes on a Linux file system

chattr [OPTION]... [+-=][ATTRIBUTES]... FILE...

Change group ownership of files or directories

chgrp [OPTION]... GROUP FILE...
chgrp [OPTION]... --reference=RFILE FILE...

Tool for managing services in SysV init systems

chkconfig [--list] [--type type] [name]
chkconfig --add name
chkconfig --del name
chkconfig [--level levels] name <on|off|reset|resetpriorities>

Change file mode bits (permissions)

chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...

Change file owner and group

chown [OPTION]... [OWNER][:[GROUP]] FILE...
chown [OPTION]... --reference=RFILE FILE...

Update passwords in batch mode

chpasswd [options]

Run command or interactive shell with special root directory

chroot [OPTION] NEWROOT [COMMAND [ARG]...]

Calculate CRC checksum and byte count for a file

cksum [OPTION]... [FILE]...

Clear the terminal screen

clear [OPTION]

Compare two files byte by byte

cmp [OPTION]... FILE1 [FILE2 [SKIP1 [SKIP2]]]

The <code>col</code> command filters reverse line feeds and converts whitespace in its input to spaces or tabs. It's primarily used to process text files containing backspace characters and other control characters often generated by certain text processors.

col [OPTION]...

Compare two sorted files line by line

comm [OPTION]... FILE1 FILE2

Run a command, ignoring shell functions and aliases

command [-pVv] command [arg ...]

Compress files using the Lempel-Ziv coding

compress [-cfvd] [-b bits] [file ...]

The <code>cp</code> command is used to copy files and directories from one location to another. It's one of the core utilities in Linux and Unix-like operating systems that supports various options for preserving attributes, handling symbolic links, and creating backups.

cp [OPTION]... SOURCE... DIRECTORY
cp [OPTION]... -t DIRECTORY SOURCE...

Copy files to and from archives

cpio {-o|--create} [-0acvABLV] [-C bytes] [-H format] [-M message] [-O [[user@]host:]archive] [-F [[user@]host:]archive] [--file=[[user@]host:]archive] [--format=format] [--message=message] [--null] [--reset-access-time] [--verbose] [--dot] [--append] [--block-size=blocks] [--dereference] [--io-size=bytes] [--quiet] [--force-local] [--rsh-command=command] [--help] [--version] < name-list [> archive]

cpio {-i|--extract} [-bcdfmnrtsuvBSV] [-C bytes] [-E file] [-H format] [-M message] [-R [user][:.][group]] [-I [[user@]host:]archive] [-F [[user@]host:]archive] [--file=[[user@]host:]archive] [--make-directories] [--nonmatching] [--preserve-modification-time] [--numeric-uid-gid] [--rename] [--list] [--swap-bytes] [--swap] [--dot] [--unconditional] [--verbose] [--block-size=blocks] [--swap-halfwords] [--io-size=bytes] [--pattern-file=file] [--format=format] [--owner=[user][:.][group]] [--no-preserve-owner] [--message=message] [--force-local] [--no-absolute-filenames] [--sparse] [--only-verify-crc] [--quiet] [--rsh-command=command] [--help] [--version] [pattern...] [< archive]

cpio {-p|--pass-through} [-0adlmuvLV] [-R [user][:.][group]] [--null] [--reset-access-time] [--make-directories] [--link] [--preserve-modification-time] [--unconditional] [--verbose] [--dot] [--dereference] [--owner=[user][:.][group]] [--no-preserve-owner] [--sparse] [--help] [--version] destination-directory < name-list

Schedule and manage cron jobs

crontab [-u user] file
crontab [-u user] [-l | -r | -e] [-i]

Split a file into sections determined by context lines

csplit [OPTION]... FILE PATTERN...

The <code>curl</code> command is a versatile tool for transferring data to or from a server using various protocols. It supports HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, DICT, TELNET, LDAP, POP3, IMAP, SMTP, and many more. Primarily used for testing APIs, downloading files, and data transfer operations without user interaction.

curl [options] [URL...]

The <code>cut</code> command is used to extract sections from each line of input. It can extract by character position, field separated by a delimiter, or bytes.

cut OPTION... [FILE]...

The <code>cvt</code> command calculates VESA CVT (Coordinated Video Timing) modelines for use with X server. It generates the appropriate modeline parameters for a given resolution and refresh rate.

cvt width height [refresh]

The <code>date</code> command displays or sets the system date and time. It can format the output in various ways, convert between time zones, and perform date arithmetic.

date [OPTION]... [+FORMAT]
date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

The <code>dc</code> command is an arbitrary precision calculator with reverse Polish notation. It supports unlimited precision arithmetic and features both interactive and script-based usage.

dc [options] [file...]

The <code>dd</code> command is a powerful utility for converting and copying files with the ability to manipulate the data as it is being copied. It's often used for tasks such as backing up boot sectors, creating disk images, and performing low-level operations on storage devices.

dd [OPERAND]...

The <code>debootstrap</code> command is used to install a basic Debian or Ubuntu system into a subdirectory of another, already installed system. It can be used to create a chroot environment, a container base image, or the first stage of a Debian-based operating system installation.

debootstrap [options] suite target [mirror [script]]

The <code>declare</code> command is a built-in shell command in Bash that declares variables and sets their attributes. It allows for specifying variable types and properties, providing more control over how variables behave in shell scripts.

declare [options] [name[=value]]...

Remove a group from the system

delgroup [options] GROUP

The <code>deluser</code> command is used to remove users from the system. It is a friendlier frontend to the <code>userdel</code> command, providing additional options to manage user removal, including handling of the user's home directory and mail spool.

deluser [options] user
deluser --group [options] group

Generate a dependency file for kernel modules

depmod [options] [version]

Report file system disk space usage

df [OPTION]... [FILE]...

Compare files line by line

diff [OPTION]... FILES

Compare three files line by line

diff3 [OPTION]... MYFILE OLDFILE YOURFILE

Query DNS servers for various DNS records and perform DNS lookups

dig [@server] [name] [type] [options]

List directory contents, similar to the ls command

dir [OPTION]... [FILE]...

Set up color configuration for ls command output

dircolors [OPTION]... [FILE]

Strip last component from a file path, returning the directory part

dirname [OPTION] NAME...

Display the list of currently remembered directories in the directory stack

dirs [OPTION]

Display or control the kernel ring buffer messages

dmesg [options]

Display hardware information from the BIOS/UEFI DMI tables

dmidecode [options]

Low-level logical volume management tool for Device Mapper

dmsetup [options] [command] [command_args]

Convert text file line endings from DOS/Windows format to Unix format

dos2unix [options] [file ...]

Estimate file space usage for files and directories

du [OPTION]... [FILE]...

Backup utility for ext2/3/4 filesystems

dump [-level] [-flags] filesystem [files-to-dump]

Dump ext2/ext3/ext4 filesystem information

dumpe2fs [options] device

The <code>echo</code> command displays text or variables to standard output. It is one of the simplest yet most frequently used commands in shell scripting, allowing users to print messages, variable values, or command outputs to the terminal or redirect them to files.

echo [OPTION]... [STRING]...

Line-oriented text editor

ed [options] [file]

Search for patterns using extended regular expressions

egrep [options] pattern [file...]

Eject removable media such as CD/DVD discs or USB drives

eject [options] [device]

Enable and disable shell built-in commands

enable [-a] [-dnps] [-f filename] [name ...]

Display, set, or remove environment variables

env [option]... [name=value]... [command [args]...]

Display or modify Ethernet device settings

ethtool [options] devname

Execute arguments as a shell command

eval [arguments]

Replace the current shell process with a specified command

exec [-cl] [-a name] [command [arguments...]]

Exit the shell with a status code

exit [n]

The <code>expand</code> command converts tabs in files to spaces. It's useful for ensuring consistent text formatting and making files more compatible with various text editors or display environments that might handle tabs differently.

expand [OPTION]... [FILE]...

Set environment variables for child processes

export [-fn] [name[=value] ...] or export -p

Evaluate expressions and display the results

expr EXPRESSION

The FALSE command in Linux

false [options]

Manipulate disk partition table

fdisk [options] [device]

Move job to the foreground

fg [job_spec]

Search for fixed strings in files

fgrep [options] pattern [file...]

Determine file type

file [options] [file...]

The <code>find</code> command is used to search for files and directories in a directory hierarchy based on various criteria. It's one of the most powerful and flexible commands for locating files in a Linux/Unix system.

find [starting-point...] [expression]

Display information about system users

finger [options] [user[@host]]

Manage file locks from shell scripts

flock [options] file|directory command [arguments]

The <code>fmt</code> command is a simple text formatter that rewraps text paragraphs to fit within specified width limits. It's useful for formatting documentation, README files, and other plain text content to improve readability.

fmt [OPTION]... [FILE]...

Wrap input lines to fit specified width

fold [options] [file...]

Shell loop construct for iterating through lists

for name [in words ...]; do commands; done
for (( expr1; expr2; expr3 )); do commands; done

Display amount of free and used memory in the system

free [options]

Check and repair a Linux filesystem

fsck [options] [filesystem...]

Display status information about open files

fstat [-f filename] [-M core] [-N system] [-p pid] [-u user] [file ...]

The <code>ftp</code> command is a standard network file transfer program that allows you to transfer files between your local machine and remote servers using the File Transfer Protocol (FTP). It provides both interactive and automated modes for transferring files, managing directories, and controlling file permissions on remote servers.

ftp [options] [host [port]]

The <code>fuser</code> command identifies processes using files or sockets. It helps you find which processes are accessing specific files, directories, or sockets, making it useful for troubleshooting and system administration. You can also use it to send signals to these processes, allowing you to terminate applications that are preventing operations like unmounting filesystems.

fuser [options] file|directory... 
fuser [options] [-n namespace] name...

Pattern scanning and processing language - GNU version

gawk [options] -f program-file [file...]

Query system configuration variables

getconf [options] variable_name [pathname]

Get entries from administrative database

getent database [key...]

Display file access control lists

getfacl [options] file ...

Parse command options in shell scripts

getopts optstring name [arg...]

Administer the /etc/group file

gpasswd [option] group

The <code>grep</code> command is used to search for text patterns in files. It's a powerful tool for finding specific content in files or filtering command output based on regular expressions or string patterns.

grep [options] pattern [file...]

The <code>groff</code> command (GNU troff) is a document formatting system that converts marked-up text files to formatted documents for display or printing. It's used for creating man pages, technical documentation, and other formatted documents with precise typographical control.

groff [OPTION]... [FILE]...

Print the groups a user is in

groups [username...]

Install GRUB bootloader on a device

grub-install [options] [--target=target] [device]

Generate a GRUB configuration file

grub-mkconfig [options]

Decompress files compressed with gzip

gunzip [options] [file...]

Compress or decompress files

gzip [options] [files...]

Stop the system

halt [options]

Display or manipulate the bash command hash table

hash [-lr] [-p pathname] [-dt] [name]

Output the first part of files

head [options] [file...]

The <code>help</code> command displays information about built-in shell commands. It provides a quick way to access documentation on bash shell commands directly from the terminal, showing their purpose, syntax, and available options.

help [PATTERN...]

Display file contents in hexadecimal, decimal, octal, or ASCII

hexdump [options] file

Display or manipulate the command history list

history [options] [n]

Show or set the system hostname

hostname [options] [name]

The <code>htop</code> command is an enhanced interactive process viewer for Linux systems. It provides a full-color terminal interface that displays system summary information and a list of processes in a more user-friendly way than the traditional top command. htop offers advanced features like vertical and horizontal scrolling, tree view, and mouse operation.

htop [options]

Query or set the hardware clock (RTC)

hwclock [options]

Convert text from one character encoding to another

iconv [options] [-f from-encoding] [-t to-encoding] [input-file]...

Display user identity information

id [options] [username]

Configure or display network interface parameters

ifconfig [interface] [options] [address]

Take down a network interface

ifdown [options] [interface]

Bring up a network interface

ifup [options] [interface]

Capture an X server screen and save the image to a file

import [options] filename

The <code>info</code> command provides access to the GNU Info system, which offers comprehensive hypertext documentation for many GNU utilities and programs. Unlike <code>man</code> pages, which typically offer concise reference material, Info documents are more extensive, structured hierarchically, and include hyperlinks for easier navigation between topics.

info [OPTION]... [MENU-ITEM...]

Wait for changes to files using inotify

inotifywait [options] [file/directory...]

Gather filesystem access statistics using inotify

inotifywatch [options] [file/directory...]

Copy files and set attributes

install [options] source... destination

Report CPU statistics and input/output statistics for devices and partitions

iostat [options] [device...] [interval [count]]

Show / manipulate routing, network devices, interfaces and tunnels

ip [options] object [command [arguments]]

Calculate IP address information

ipcalc [options] [ip_address[/prefix]]

Measure network performance

iperf [-s|-c host] [options]

A collection of utilities for controlling TCP/IP networking and traffic control in Linux

Various commands including ip, tc, ss, bridge, rtacct, rtmon, etc.

Administration tool for IPv4 packet filtering and NAT

iptables [-t table] command [chain] [rule-specification] [options]

Interactive colorful IP LAN monitor

iptraf [-h|-f|-z|-i interface|-g|-d interface|-s interface|-l|-t facility]

Display status of jobs in the current shell session

jobs [-lnprs] [jobspec]

Join lines of two files on a common field

join [options] file1 file2

Query and display messages from the systemd journal

journalctl [OPTIONS...] [MATCHES...]

A collection of tools for managing Linux console (keyboard and fonts)

Various commands including loadkeys, setfont, showkey, etc.

Destroy Kerberos tickets

kdestroy [-A] [-q] [-c cache_name] [-p principal_name]

TCP keepalive configuration utility for network connections

keepalive [options]

The <code>kill</code> command is used to send signals to processes, typically to terminate them. By default, it sends the TERM (terminate) signal, but it can send any specified signal to a process identified by its process ID (PID). The kill command is essential for process management and system administration tasks.

kill [options] PID...

The <code>killall</code> command terminates processes by name rather than by process ID (PID). It can kill multiple processes with the same name simultaneously, making it more convenient than the <code>kill</code> command when you don't know or don't want to look up process IDs. Like <code>kill</code>, it can send any signal to the specified processes.

killall [options] name...

Obtain and cache Kerberos ticket-granting ticket

kinit [options] [principal]

List Kerberos tickets in credential cache

klist [options]

Manage Linux kernel modules

kmod [options] command [command_options]

Show listing of last logged in users

last [options] [username...] [tty...]

Show listing of last bad login attempts

lastb [options] [username...] [tty...]

Display information about the most recent login of all users

lastlog [options]

File pager that allows backward and forward navigation through file contents

less [options] file...

Perform arithmetic operations on shell variables

let expression [expression ...]

Create a hard link to a file

link source_file target_file

The <code>ln</code> command is used to create links between files in Linux/Unix systems. It can create both hard links and symbolic (soft) links, allowing multiple filenames to point to the same file or directory.

ln [OPTION]... [-T] TARGET LINK_NAME
ln [OPTION]... TARGET
ln [OPTION]... TARGET... DIRECTORY
ln [OPTION]... -t DIRECTORY TARGET...

Load keyboard translation tables

loadkeys [options] [keymap]

The <code>locate</code> command quickly finds files by name on a Linux system. It searches a database built by <code>updatedb</code> rather than scanning the filesystem in real-time, making it much faster than <code>find</code> for basic file name searches.

locate [OPTION]... PATTERN...

Add entries to the system log

logger [options] [message]

Begin a session on the system

login [options] [username]

Print the name of the current user

logname [options]

Exit a login shell

logout

Display lines beginning with a given string

look [options] string [file]

Set up and control loop devices

losetup [options] [loopdev] [file]

Line printer control program

lpc [command [argument ...]]

Print files

lpr [options] [file...]

Print a file

lprint [options] [file...]

Abort a print job

lprintd [options] [job_id...]

List the print queue

lprintq [options]

Remove jobs from the print queue

lprm [options] [job_id...]

The <code>ls</code> command is one of the most basic and frequently used commands in Linux/Unix systems. <code>ls</code> stands for "list" and it lists the contents of directories, showing files and subdirectories.

ls [OPTION]... [FILE]...

List file attributes on a Linux file system

lsattr [options] [files...]

List information about block devices

lsblk [options] [device...]

Display information about the CPU architecture

lscpu [options]

List hardware information

lshw [options]

Display information about user accounts

lslogins [options] [username...]

Show the status of loaded kernel modules

lsmod

List open files

lsof [options]

List all PCI devices

lspci [options]

List SCSI devices or hosts

lsscsi [options]

List USB devices

lsusb [options]

A library call tracer

ltrace [options] [command [arg...]]

Macro processor

m4 [options] [files]

Build automation tool

make [options] [target...]

The <code>man</code> command is used to display the manual pages (documentation) for commands, utilities, functions, and files in Unix-like operating systems. It provides a standardized way to access comprehensive documentation for almost every command and feature available on the system.

man [OPTION]... [SECTION] NAME...

The <code>mandb</code> command creates or updates the manual page index caches (databases) used by <code>man</code>, <code>apropos</code>, and <code>whatis</code>. It indexes the contents of all manual pages to enable fast searching based on names, descriptions, and keywords.

mandb [OPTION...]

Read lines from standard input into an indexed array variable

mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]

Compute and check MD5 message digest

md5sum [OPTION]... [FILE]...

Display disk usage in megabytes

mdu [options] [file...]

Control write access to your terminal

mesg [y|n]

The <code>mkdir</code> command is used to create directories (folders) in Linux/Unix systems. <code>mkdir</code> stands for "make directory" and is essential for organizing files and creating new storage locations.

mkdir [OPTION]... DIRECTORY...

Create an ext2/ext3/ext4 filesystem

mke2fs [options] device [blocks-count]

Make FIFOs (named pipes)

mkfifo [OPTION]... NAME...

Make block or character special files

mknod [OPTION]... NAME TYPE [MAJOR MINOR]

Create a temporary file or directory

mktemp [OPTION]... [TEMPLATE]

The <code>mlocate</code> command (Merging Locate) is a secure implementation of the locate command that maintains file ownership/permission information and merges new file entries incrementally. It provides a fast way to search the filesystem by using a previously built database.

mlocate [OPTION]... PATTERN...

Move/rename multiple files using patterns

mmv [options] from_pattern to_pattern

Display file content one screen at a time

more [options] [file...]

Mount a filesystem

mount [-t fstype] [-o options] device dir

Network diagnostic tool combining ping and traceroute

mtr [options] hostname

Text-based email client for Unix-like systems

mutt [options] [-Z] [-f mailbox] [-e command] [--] [addresses...]

The <code>mv</code> command is used to move or rename files and directories in Linux and Unix-like operating systems. It can move files between directories and rename them in a single operation while preserving file attributes.

mv [OPTION]... SOURCE... DIRECTORY
mv [OPTION]... -t DIRECTORY SOURCE...

Check, repair, or optimize MyISAM tables in MySQL databases

myisamchk [options] tbl_name [...]

Display contents of MyISAM log file

myisamlog [options] [log_file [table_name] ...]

Follow a pathname until a terminal point is found

namei [options] pathname [pathname...]

A simple command-line text editor

nano [options] [[+line[,column]] file]...

Netcat utility for reading from and writing to network connections

nc [options] [hostname] [port]

Networking utility for reading from and writing to network connections

netcat [options] [hostname] [port]

Display network connections, routing tables, interface statistics, masquerade connections, and multicast memberships

netstat [options]

Run a command with modified scheduling priority

nice [option] [command [arguments...]]

Number lines of files

nl [options] [file]

Network exploration tool and security scanner

nmap [scan type] [options] {target specification}

Run a command immune to hangups, with output to a non-tty

nohup COMMAND [ARG]...

Print the number of processing units available

nproc [OPTION]

The <code>nroff</code> command is a text formatting program for Unix/Linux that formats documents for display on terminals and line printers. It's a component of the groff document formatting system specifically tailored for producing plain text output.

nroff [OPTION]... [FILE]...

Query Internet name servers for domain name or IP address mapping

nslookup [options] [hostname/IP] [server]

Fix common errors and force Windows to check NTFS filesystem

ntfsfix [options] device

Set the system date and time via NTP

ntpdate [options] server [server...]

NTP query utility for monitoring NTP daemon ntpd operations

ntpq [options] [host...]

Control NUMA policy for processes or shared memory

numactl [options] -- program [arguments]

Copy and translate object files

objcopy [options] input-file [output-file]

Display information from object files

objdump [options] file...

Dump files in octal and other formats

od [options] [file...]

Open files, directories, or URLs with default applications

open [options] file/URL...

Cryptography and SSL/TLS toolkit

openssl command [command_options] [command_arguments]

Secure Virtual Private Network daemon

openvpn [options] [config_file]

Lightweight package management system for embedded Linux devices

opkg [options] sub-command [arguments]

A disk partition manipulation program

parted [options] [device [command [arguments]...]]

Change user password

passwd [options] [username]

Merge lines of files horizontally

paste [options] [file...]

Apply a diff file to an original

patch [options] [originalfile [patchfile]]

Check whether file names are valid or portable

pathchk [options] name...

Performance analysis tool for Linux

perf [--version] [--help] [OPTIONS] COMMAND [ARGS]

The Perl 5 language interpreter

perl [options] [program_file] [arguments]

Extract a PostgreSQL database into a script file or other archive file

pg_dump [connection-option...] [option...] [dbname]

Restore a PostgreSQL database from an archive file created by pg_dump

pg_restore [connection-option...] [option...] [filename]

Send ICMP ECHO_REQUEST to network hosts

ping [options] destination

The <code>pkill</code> command sends signals to processes based on their name and other attributes. It's a more flexible alternative to <code>killall</code>, allowing pattern matching and filtering by various process attributes like terminal, parent PID, user, and more. This makes it a powerful tool for targeted process management.

pkill [options] pattern

Remove a directory from the directory stack

popd [+N | -N]

The <code>pr</code> command formats text files for printing. It can paginate text with headers and footers, create multi-column output, merge files side by side, and adjust various formatting elements like margins and page length.

pr [OPTION]... [FILE]...

Print all or part of the environment

printenv [OPTION]... [VARIABLE]...

Format and print data

printf FORMAT [ARGUMENT]...

The <code>ps</code> command displays information about active processes running on the system. It provides a snapshot of the current processes along with detailed information about resource usage, status, and other process attributes.

ps [options]

Display a tree of processes

pstree [options] [pid|user]

Print name of current/working directory

pwd [OPTION]...

Quick Emulator, a generic machine emulator and virtualizer

qemu-system-[arch] [options] [disk_image]

Display disk usage and limits for a user or group

quota [options] [user|group]

Scan a filesystem for disk usage and create, check, or repair quota files

quotacheck [options] [filesystem...]

Manipulate disk quotas

quotactl command special [id quota]

Create a RAM disk or display information about RAM disks

ram [options] size

Create and manage RAM-based virtual disk drives

ramdisk [options] [size]

Read a line from standard input or a file descriptor

read [options] [variable...]

Read lines from standard input into an array variable

readarray [options] array

Mark variables or functions as read-only

readonly [options] [name[=value] ...]

Restart the system

reboot [options]

Rename multiple files using pattern substitution

rename [options] expression replacement file...

Alter priority of running processes

renice priority [[-p] pid...] [[-g] pgrp...] [[-u] user...]

Repartition a disk or update partition tables

repart [options] device

Reset the terminal

reset [options]

Reverse lines of a file or standard input

rev [file...]

The <code>rm</code> command is used to remove files and directories in Linux/Unix systems. <code>rm</code> stands for "remove" and it's a powerful command that can delete files, directories, and their contents permanently.

rm [OPTION]... [FILE]...

The <code>rmdir</code> command is used to remove empty directories from the filesystem in Linux/Unix systems. <code>rmdir</code> stands for "remove directory" and is a safe way to delete directories as it will only work if the directory is empty.

rmdir [OPTION]... DIRECTORY...

The <code>rsync</code> command is a fast, versatile file copying and synchronization tool that efficiently transfers and synchronizes files between directories or across computers. It is widely used for backups, mirroring, and maintaining identical copies of data.

rsync [OPTION]... SRC [SRC]... DEST
rsync [OPTION]... SRC [SRC]... [USER@]HOST:DEST
rsync [OPTION]... [USER@]HOST:SRC [DEST]

Enter a system sleep state until specified wakeup time

rtcwake [options]

Display the current and previous system runlevel

runlevel [options]

Run a command with substitute user and group ID

runuser [options] -u user [--] [command [args...]]

Collect, report, or save system activity information

sar [options] [interval [count]]

The <code>scp</code> (Secure Copy) command is used to securely transfer files between hosts on a network. It uses SSH for data transfer and provides the same authentication and security as SSH. SCP is ideal for safely copying files across untrusted networks.

scp [OPTION] [[user@]src_host:]file1 ... [[user@]dst_host:]file2

Side-by-side merge of file differences

sdiff [options] file1 file2

The <code>sed</code> command (stream editor) is used for parsing and transforming text files line by line. It's a powerful tool for text manipulation that performs operations like search, find and replace, insertion, and deletion on text streams.

sed [OPTION]... {script} [input-file]...
sed [OPTION]... -f script-file [input-file]...

Create an interactive selection menu in the shell

select name [in words ...]; do commands; done

Print a sequence of numbers

seq [options] [first [increment]] last

Set or unset shell options and positional parameters

set [options] [arguments]

Set file access control lists (ACLs)

setfacl [options] acl_spec file...

The <code>sftp</code> (Secure File Transfer Protocol) command provides an interactive file transfer program with functionality similar to FTP but operates over an encrypted SSH connection. It offers secure file transfer capabilities with additional features like resuming transfers and directory operations.

sftp [OPTION] [[user@]host[:file [file]]]

Shift positional parameters in a shell script

shift [n]

Set and unset shell options

shopt [-pqsu] [-o] [optname...]

Shut down, reboot, or halt the system

shutdown [options] [time] [message]

Delay for a specified amount of time

sleep number[suffix]...

Sort lines of text files

sort [options] [file...]

Execute commands from a file in the current shell

source filename [arguments]

Split a file into pieces

split [options] [input [prefix]]

Command-line interface for SQLite 3 databases

sqlite3 [options] [database] [SQL statements]

The <code>ssh</code> (Secure Shell) command is a secure protocol used to remotely connect to and manage systems over an encrypted network connection. It allows for secure remote logins, command execution, file transfers, and port forwarding with strong encryption and authentication mechanisms.

ssh [options] [user@]hostname [command]

The <code>ssh-add</code> command adds SSH private keys to the SSH authentication agent (ssh-agent). It allows you to load your keys into memory so you can use SSH without entering your passphrase each time, while keeping your keys securely encrypted on disk.

ssh-add [options] [file ...]

The <code>ssh-agent</code> command starts an authentication agent that can store private keys for SSH authentication. It allows users to authenticate to SSH servers without having to constantly re-enter their private key passphrase, providing both convenience and security by keeping keys encrypted on disk but available for use during a session.

ssh-agent [options] [command [args ...]]

The <code>ssh-copy-id</code> command installs an SSH public key on a remote server as an authorized key. This enables secure passwordless SSH logins to the remote system, allowing you to authenticate using your private key instead of typing your password each time.

ssh-copy-id [options] [-i [identity_file]] [user@]hostname

The <code>ssh-keygen</code> command is used to generate, manage, and convert authentication keys for SSH (Secure Shell). It creates public/private key pairs for secure passwordless authentication, and provides various options for key type selection, key conversion, and key management.

ssh-keygen [options]

Display file or file system status

stat [options] file...

Trace system calls and signals

strace [options] [command [args]]

Print the printable character sequences in files

strings [options] [file...]

Switch user or substitute user

su [options] [username]

Execute a command as another user

sudo [options] [command]

Compute checksum and count blocks in a file

sum [options] [file...]

Control services monitored by supervise or daemontools

svc [options] service_directories...

Disable devices and files for swapping

swapoff [options] [special]

Enable devices and files for swapping

swapon [options] [special]

Synchronize cached writes to persistent storage

sync [options] [file...]

Configure kernel parameters at runtime

sysctl [options] [variable[=value]] [...]

Control the systemd system and service manager

systemctl [options] command [name...]

System and service manager for Linux operating systems

systemd [options...]

View and manage sysfs devices, buses, drivers, and modules

systool [options] [path...]

Concatenate and print files in reverse (opposite of cat)

tac [OPTION]... [FILE]...

Output the last part of files

tail [OPTION]... [FILE]...

Tape Archive: create, extract, and manipulate archive files

tar [options] [archive-file] [file or directory to be archived]

Set or retrieve a process's CPU affinity

taskset [options] mask command [argument...]
taskset [options] -p [mask] pid

Dump network traffic, analyze and capture packets

tcpdump [options] [expression]

The <code>tee</code> command reads from standard input and writes to both standard output and one or more files simultaneously. This allows you to view output in your terminal while also saving it to a file, making it invaluable for logging and debugging.

tee [OPTION]... [FILE]...

Change SysV init runlevel or systemd system state

telinit [option] <runlevel>

Check file types and compare values

test EXPRESSION
[ EXPRESSION ]
[ OPTION

Measure program execution time

time [options] command [arguments...]

Run a command with a time limit

timeout [OPTION] DURATION COMMAND [ARG]...

Display process time information for the current shell and its children

times

The <code>top</code> command provides a dynamic real-time view of a running system. It displays system summary information and a list of processes or threads currently being managed by the Linux kernel. It shows CPU usage, memory usage, swap usage, and the most CPU-intensive tasks running on the system, all updated in real-time.

top [options]

Change file timestamps or create empty files

touch [OPTION]... FILE...

The <code>tr</code> command (translate) is used to translate, squeeze, and/or delete characters from standard input, writing to standard output. It's a simple yet powerful tool for character-level text transformations.

tr [OPTION]... SET1 [SET2]

Print the route packets take to a network host

traceroute [options] host [packetsize]

Set up signal handlers in shell scripts

trap [OPTIONS] [[ARG] SIGNAL...]

The <code>troff</code> command (typesetter roff) is a document formatting system for Unix-like operating systems that formats text for typesetter and printing devices. It's the foundation of the groff formatting system and provides detailed control over document typography and layout.

troff [OPTION]... [FILE]...

The TRUE command in Linux

true [options]

Add timestamp to each line of input

ts [options] [format]

Print the file name of the terminal connected to standard input

tty [OPTION]...

Create and manage persistent TUN/TAP interfaces

tunctl [-t device-name] [-u owner] [-g group] [-b] [-f tun-clone-device] [-d device-name]

Display information about command type

type [-afptP] name [name ...]

udev management tool for device detection and configuration

udevadm [--help] [--version] [--debug] COMMAND [OPTIONS]

Get and set user limits for system resources

ulimit [-HSabcdefiklmnpqrstuvxPT] [limit]

Set file mode creation mask

umask [-p] [-S] [mode]

Unmount file systems

umount [options] <source> | <directory>

Print system information

uname [OPTION]...

The <code>unexpand</code> command converts spaces in files to tabs. It's the counterpart to the expand command and is useful for reducing file size or formatting files according to specific requirements that prefer tabs over spaces.

unexpand [OPTION]... [FILE]...

Report or omit repeated lines

uniq [OPTION]... [INPUT [OUTPUT]]

Convert quantities between different units

units [options] [from-unit [to-unit]]

Remove variable or function names from the shell environment

unset [-fv] [name ...]

Run program in new namespaces

unshare [options] [program [arguments]]

Execute commands until a condition is true

until test-commands; do consequent-commands; done

The <code>updatedb</code> command updates the file name database used by the <code>locate</code> command. It scans your filesystem and builds a database of file names and locations, which allows for fast file searches without having to scan the filesystem in real-time.

updatedb [OPTION...]

Tell how long the system has been running

uptime [options]

Create a new user or update default new user information

useradd [options] LOGIN

Delete a user account and related files

userdel [options] LOGIN

Modify a user account

usermod [options] LOGIN

Print the usernames of users currently logged in

users [OPTION]... [FILE]

Suspend execution for microsecond intervals

usleep microseconds

Display file system statistics

ustat [-fv] device

Decode a file created by uuencode

uudecode [options] [file...]

Encode a binary file into ASCII for transmission

uuencode [-m] [file] name

List directory contents in a verbose, multi-column format

vdir [OPTION]... [FILE]...

Screen-oriented (visual) text editor

vi [options] [file...]

Vi IMproved, a programmers text editor

vim [options] [file...]

Report virtual memory statistics

vmstat [options] [delay [count]]

Return volume name for a device

volname [device]

Client for Cisco VPN concentrator

vpnc [options] [config file]

Show who is logged on and what they are doing

w [options] [user]

Wait for process completion and return exit status

wait [options] [id...]

Execute a program periodically, showing output fullscreen

watch [options] command

Print newline, word, and byte counts for files

wc [OPTION]... [FILE]...

The <code>wget</code> command is a non-interactive network downloader that retrieves files from the web. It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies. Unlike interactive browsers, wget can work in the background, after users log off, retrieving files recursively and creating local versions of remote sites.

wget [options] [URL...]

The <code>whatis</code> command displays brief manual page descriptions. It searches the manual page names and displays a brief description from the manual page header. This is particularly useful for quickly finding out what a command does without reading the full manual page.

whatis [OPTION]... KEYWORD...

Locate the binary, source, and manual page files for a command

whereis [options] name...

The <code>which</code> command locates the executable file associated with a given command by searching the directories listed in the PATH environment variable. It helps determine which version of a program will be executed when you type a command in the terminal.

which [OPTION]... COMMAND...

Show who is logged on the system

who [OPTION]... [FILE | ARG1 ARG2]

Print effective username

whoami [OPTION]...

Send a message to another user

write user [ttyname]

Build and execute command lines from standard input

xargs [options] [command [initial-arguments]]

Command line interface to X clipboard selections

xclip [options]

Open a file or URL with the default application

xdg-open {file|URL}

XFS filesystem utilities and commands

xfs tools are a suite of commands: xfs_admin, xfs_repair, xfs_db, etc.

Check XFS filesystem consistency (deprecated in favor of xfs_repair)

xfs_check [-f] [-i ino]... [-b bno]... special

Repair an XFS filesystem

xfs_repair [-nfdPLvVm] [-o options] [-l logdev] [-r rtdev] [-t interval] device

A utility to configure and test X input devices

xinput [options] [command] [device]

Force close unresponsive X clients by killing their associated windows

xkill [-button number] [-frame] [-id resource] [-all] [-display displayname]

Command line interface to X RandR extension for screen resolution and display configuration

xrandr [options] [--output output] [output-options]

Extensible screen saver and locker for the X Window System

xscreensaver [options]

User preference utility for X Window System

xset [options]

Output a string repeatedly until killed

yes [STRING]...
yes [OPTION]

NIS (Network Information Service) client process that binds to an NIS server

ypbind [options]

Print the values of all keys in an NIS (Network Information Service) database

ypcat [options] mapname

Print the values of one or more keys from an NIS (Network Information Service) map

ypmatch [options] key... mapname

Change your network password in the NIS (Network Information Service) database

yppasswd [user]

Return hostname of NIS server or map master

ypwhich [options] [host]
ypwhich [-m [mapname]]

Package manager for RPM-based Linux distributions

yum [options] command [package...]

Display the contents of compressed files without explicitly decompressing them

zcat [options] [file...]

Compare compressed files

zdiff [options] file1 file2
zcmp [options] file1 file2

Search compressed files for extended regular expressions

zegrep [options] pattern [file...]

Search compressed files for fixed strings

zfgrep [options] pattern [file...]

Force a .gz extension on gzip compressed files

zforce [file...]

Search compressed files for a regular expression

zgrep [options] pattern [file...]

Package and compress (archive) files

zip [options] zipfile files...

View compressed files with the less pager

zless [options] file...

View compressed files with the more pager

zmore [file...]

Recompress .Z files to .gz format

znew [options] [file.Z...]

Z Shell - an extended Bourne shell with numerous improvements and additional features

zsh [options] [file [arguments...]]