Ultimate A‑Z Linux Command Cheat Sheet: Master System Operations

A

access : Checks whether a program can access a specified file, also used to test file existence.

accton : Starts or stops the accounting process or changes the accounting file.

aclocal : Automatically generates the aclocal.m4 file from configure.in.

acpi : Displays battery status and other ACPI information.

acpi_available : Tests whether the ACPI subsystem is available.

acpid : Provides intelligent power management, notifying user‑space programs of ACPI events.

addr2line : Converts an address into a file name and line number.

agetty : Manages physical or virtual terminals to allow multi‑user access.

alias : Replaces a string with another when a command is executed.

amixer : Command‑line mixer for ALSA sound drivers.

aplay : Command‑line audio player for ALSA sound drivers.

aplaymidi : Plays standard MIDI files via ALSA MIDI ports.

apropos : Helps users find commands when they remember keywords but not the exact name.

apt : High‑level CLI for package management, intended for end users.

apt-get : Command‑line tool for handling packages in Linux.

aptitude : Interactive interface for the package manager.

ar : Creates, modifies, and extracts files from archives.

arch : Prints the computer architecture.

arp : Manipulates the ARP cache, allowing full dump of the cache.

aspell : Spell checker for Linux.

atd : Job‑scheduling daemon that runs scheduled jobs later.

atrm : Removes specified jobs by job number.

atq : Shows the list of pending jobs for the user.

autoconf : Generates configuration scripts.

autoheader : Creates template header files for configure.

automake : Automatically generates GNU‑standard Makefile.in files.

autoreconf : Creates automatically buildable source code for Unix‑like systems.

autoupdate : Updates configure.in files to newer Autoconf versions.

awk : Scripting language for data manipulation and report generation.

B

banner : Prints a large ASCII string to standard output.

basename : Strips directory and suffix from a filename, printing the base name.

batch : Reads commands from standard input or a file and executes them when system load permits (average load < 1.5).

bc : Command‑line calculator.

bg : Moves a foreground job to the background.

biff : Mail notification system that alerts users of new mail.

bind : Sets Readline key bindings and variables.

bison : Parser generator similar to yacc.

break : Terminates for, while, or until loops.

builtin : Runs a shell builtin with arguments and returns its exit status.

bzcmp : Calls cmp on bzip2‑compressed files.

bzdiff : Compares bzip2‑compressed files.

bzgrep : Searches patterns in bzip2‑compressed files.

bzip2 : Compresses and decompresses files.

bzless : Faster viewing of large compressed files without reading the entire input first.

bzmore : Filters bzip2‑compressed files for CRT viewing.

C

cal : Shows a calendar for a specific month or year; defaults to the current month.

case : Best choice when multiple if/elif conditions are needed on a single variable.

cat : Reads data from files and outputs their contents.

cc : Compiles C source code and creates executables.

ccrypt : Command‑line tool for data encryption and decryption.

cd : Changes the current working directory.

cfdisk : Text‑based graphical interface for displaying or manipulating disk partition tables.

chage : Views and modifies user password expiration information.

chattr : Changes file attributes on a filesystem.

chfn : Changes a user's full name and other details.

chgrp : Changes group ownership of files or directories.

chkconfig : Lists all available services and views/updates their run‑level settings.

chmod : Changes file access permissions.

chown : Changes file owner or group.

chpasswd : Changes passwords for multiple users at once.

chroot : Changes the root directory.

chrt : Manipulates real‑time attributes of processes.

chsh : Changes a user's login shell.

chvt : Switches between available TTY terminals.

cksum : Displays a CRC value, byte count, and filename.

clear : Clears the terminal screen.

cmp : Compares two files byte‑by‑byte.

col : Filters reverse line feeds; reads from stdin and writes to stdout.

colcrt : Formats output of text processors for CRT displays.

colrm : Removes selected columns from a file.

column : Displays file contents in columns.

comm : Compares two sorted files line by line, showing common and unique lines.

compress : Reduces file size, adding a .Z extension.

continue : Skips the current iteration of for, while, or until loops.

cp : Copies files or directories.

cpio : Handles archive files such as *.cpio or *.tar.

cpp : C preprocessor that runs before compilation.

cron : Schedules tasks to run automatically at specified times.

crontab : List of scheduled commands.

csplit : Splits a file into sections based on user‑defined criteria.

ctags : Quickly accesses file definitions, such as function definitions.

cupsd : Scheduler for the Common UNIX Printing System (CUPS).

curl : Transfers data to or from a server using supported protocols.

cut : Extracts sections from each line of a file.

cvs : Version control system that stores file history and allows rollback.

D

date : Displays or sets the system date and time.

dc : Calculator that evaluates arithmetic expressions in postfix notation.

dd : Converts and copies files; primary utility for low‑level copying.

declare : Declares shell variables and functions, sets attributes, and displays values.

depmod : Generates dependency description lists for kernel modules.

df : Shows total and available space information for filesystems.

diff : Displays differences between files by line‑by‑line comparison.

diff3 : Compares three files line by line.

dir : Lists directory contents.

dirname : Strips trailing slashes from a pathname and prints the remainder.

dirs : Shows the list of remembered directories.

disable : Stops a printer or class.

dmesg : Checks the kernel ring buffer and prints kernel messages.

dmidecode : Retrieves hardware information such as CPU, RAM, BIOS in a readable format.

domainname : Returns the NIS domain name of the host.

dos2unix : Converts DOS text files to UNIX format.

dosfsck : Diagnoses and attempts to fix MS‑DOS filesystem issues.

dstat : Retrieves statistics from system components like network, I/O, CPU.

du : Tracks files and directories consuming excessive disk space.

dump : Backs up a filesystem to a storage device.

dumpe2fs : Prints superblock and block group information of a filesystem.

dumpkeys : Dumps the keyboard translation table.

E

echo : Displays a line of text/string passed as an argument.

ed : Line‑oriented text editor with minimal interface.

egrep : Prints lines matching extended regular expressions.

eject : Software‑controlled ejection of removable media.

emacs : Text editor with a simple user interface; operates in edit mode only.

enable : Starts a printer or class.

env : Prints environment variables; can run utilities in a custom environment.

eval : Executes arguments as a shell command.

ex : Line‑editing mode of the vi editor.

exec : Executes a command from within bash itself.

exit : Exits the currently running shell.

expa : Converts tabs to spaces; reads from stdin if no file is specified.

expect : Automates scripts that require user input.

export : Marks variables for export to child processes.

expr : Evaluates expressions and displays the result.

F

factor : Prints prime factors of a given number.

fc : Lists, edits, or re‑executes previously entered commands.

fc-cache : Scans font directories and builds caches for fontconfig.

fc-list : Lists available fonts and styles, optionally filtering.

fdisk : Dialog‑driven utility for creating and manipulating disk partition tables.

fg : Brings a background job to the foreground.

fgrep : Searches for fixed strings in files.

file : Determines file type, reporting human‑readable or MIME type.

find : Searches for files and directories and performs actions on them.

finger : Provides detailed information about logged‑in users.

fmt : Formats text files for simple optimization.

fold : Wraps each line of input to a specified width.

for : Repeats a set of commands for each element in a list.

free : Shows total and used memory and swap, plus kernel buffers.

Fun : Draws various patterns on the terminal.

function : Creates functions or methods.

G

g++ : Preprocesses, compiles, assembles, and links source code to produce executables.

gawk : Pattern scanning and processing language.

gcc : GNU Compiler Collection for C, C++, Objective‑C, and more.

gdb : GNU Debugger for programs written in C, C++, Ada, Fortran, etc.

getent : Retrieves entries from various databases.

gpasswd : Manages /etc/group and /etc/gshadow.

grep : Searches files for a specific character pattern and displays matching lines.

groupadd : Creates a new user group.

groupdel : Deletes an existing group.

groupmod : Modifies an existing group.

groups : Shows groups a user belongs to.

grpck : Verifies integrity of group information.

grpconv : Converts to shadow groups.

gs : Calls Ghostscript, interpreter for PostScript and PDF.

gunzip : Compresses or expands files or file lists.

gzexe : Compresses executable files and automatically decompresses them on execution.

gzip : Compresses files, producing a .gz file.

H

halt : Instructs hardware to stop all CPU functions, leading to reboot or shutdown.

hash : Maintains a hash table of recently executed programs.

hdparm : Retrieves and changes hard‑disk statistics, write cache, acoustic management, DMA settings.

Head : Prints the first N lines of input.

help : Shows information about shell built‑in commands.

hexdump : Filters and displays files in octal or other formats.

history : Views previously executed commands.

host : Performs DNS lookup operations.

hostid : Displays the host ID in hexadecimal.

hostname : Retrieves or sets the system's DNS or NIS domain name.

hostnamectl : API for controlling the host name and related settings.

htop : Interactive real‑time system resource monitor.

hwclock : Utility for accessing the hardware (real‑time) clock.

I

iconv : Converts text from one encoding to another.

id : Shows user and group names and numeric IDs.

if : Executes commands based on a condition.

ifconfig : Configures kernel‑resident network interfaces.

iftop : Network analysis tool for bandwidth statistics.

ifup : Activates a network interface.

import : Captures a screenshot of any active page and saves it as an image file.

info : Reads documentation in info format, providing detailed command information.

insmod : Inserts a module into the kernel.

install : Copies files and sets attributes.

iostat : Monitors I/O statistics for devices and partitions.

iotop : Shows detailed disk I/O usage per process.

ip : Performs various network management tasks.

ipcrm : Removes IPC resources, cleaning up objects and related data structures.

ipcs : Displays information about IPC facilities the calling process can read.

iptables : Sets and maintains tables for the IPv4 Netfilter firewall.

iptables-save : Saves current iptables rules to a user‑specified file.

iwconfig : Shows parameters and wireless statistics from /proc/net/wireless.

J

join : Joins lines of two files based on a common field.

journalctl : Views systemd, kernel, and journal logs.

K

kill : Manually terminates processes by sending signals.

L

last : Shows a list of all users who have logged in and out since /var/log/wtmp was created.

less : Views text files one page at a time.

let : Evaluates arithmetic expressions for shell variables.

ln : Creates links between files.

locate : Finds files by name.

look : Displays lines beginning with a given string.

lsblk : Shows detailed information about block devices.

lshw : Generates detailed hardware configuration information from /proc.

lsmod : Shows status of kernel modules.

lsof : Provides a list of open files.

lsusb : Shows information about USB buses and connected devices.

M

mailq : Prints the mail queue, listing messages awaiting delivery.

man : Displays the manual page for any command.

md5sum : Verifies data integrity using the MD5 algorithm.

mkdir : Creates one or more directories.

modinfo : Shows information about a Linux kernel module.

more : Views text files one screen at a time.

mount : Mounts a filesystem found on a device into the directory tree.

mpstat : Reports processor‑related statistics.

mv : Moves one or more files or directories.

N

nc (netcat) : Powerful network, security, or monitoring tool.

netstat : Shows various network information such as connections, routing tables, interface statistics.

nmcli : Controls NetworkManager; can display device status, create, edit, activate/deactivate, and delete connections.

nslookup : Queries DNS to obtain domain name or IP address mappings.

O

od : Converts input to octal or other formats, defaulting to octal.

P

passwd : Changes a user account password.

paste : Horizontally merges files, outputting lines from each file separated by tabs.

pidof : Finds the process ID of a running program.

ping : Checks network connectivity between host and server.

pinky : Provides detailed information about logged‑in users.

pmap : Shows memory mapping of a process.

poweroff : Sends an ACPI signal to power off the system.

printf : Displays formatted strings, numbers, or other data on the terminal.

ps : Lists currently running processes with their PID and other info.

pwd : Prints the current working directory path.

R

ranlib : Generates an index to an archive.

rcp : Copies files from one computer to another.

read : Reads a specified number of bytes from a file descriptor into a buffer.

readelf : Retrieves information from ELF (Executable and Linkable Format) files.

readlink : Prints the resolved symbolic link or canonical filename.

reboot : Indicates the system should restart.

rename : Renames files using a perlexpr regular expression.

reset : Reinitializes the terminal.

restore : Restores files from a backup created with dump.

return : Exits a shell function.

rev : Reverses lines character by character.

rm : Removes files, directories, symbolic links, etc.

rmdir : Removes empty directories.

rmmod : Removes a module from the kernel.

route : Used when working with IP/kernel routing tables.

rsync : Synchronizes files and directories between two hosts.

S

sar : Monitors system resources such as CPU, memory, I/O devices.

scp : Securely copies files between servers.

screen : Allows multiple shell sessions from a single SSH session.

script : Records all terminal activity.

scriptreplay : Replays recorded terminal activity from a typescript file.

sdiff : Compares two files and writes results side‑by‑side.

sed : Finds, filters, replaces, and manipulates text.

select : Creates a numbered menu for user selection.

seq : Generates numbers from FIRST to LAST in INCREMENT steps.

setsid : Runs a program in a new session.

shift : Shifts command‑line arguments left by one position.

showkey : Prints scan codes or key codes of each pressed key.

shred : Securely deletes files from a hard drive.

shutdown : Safely shuts down the system.

sleep : Creates a virtual job to delay execution.

source : Reads and executes file contents in the current shell.

sort : Sorts files according to a specified order.

split : Splits large files into smaller pieces.

ssh : Secure protocol for connecting to remote servers.

strace : Powerful process monitoring, diagnostic, and teaching tool.

stty : Changes and prints terminal line settings.

sudo : Prefix for commands that require super‑user privileges.

sum : Finds checksums and counts blocks in a file.

sync : Writes cached data to persistent storage.

systemctl : Checks and controls the systemd system and service manager.

T

tac : Concatenates and prints files in reverse order.

tail : Prints the last N lines of input.

tar : Creates and extracts archive files.

tee : Reads standard input and writes to standard output and files.

time : Executes a command and prints a summary of real, user CPU, and system CPU time.

top : Provides a dynamic real‑time view of a running system.

touch : Creates, changes, or modifies file timestamps.

tr : Translates or deletes characters.

tracepath : Traces the path to a destination, discovering MTU along the way.

traceroute : Prints the route packets take to a host.

tree : Recursively lists directories, generating an indented file list.

tty : Shows information about the terminal associated with standard input.

type : Describes how a command name would be interpreted.

U

uname : Displays system information.

unexpand : Converts spaces to tabs, writing output to standard output.

uniq : Reports or filters out repeated lines in a file.

unix2dos : Converts Unix text files to DOS format.

until : Executes a set of commands until the last command's exit status is zero.

uptime : Shows how long the system has been running.

useradd : Adds a user account to the system.

usermod : Changes user attributes via the command line.

username : Retrieves the username and its configuration.

users : Displays usernames of users currently logged in.

userdel : Deletes a user account and related files.

V

vi : Default visual editor for UNIX systems.

vmstat : Monitors performance, showing processes, memory, paging, block I/O, and CPU scheduling.

vnstat : Monitors network parameters such as bandwidth consumption.

W

w : Shows who is logged in and what they are doing.

wall : Displays a message, file content, or stdin on all logged‑in users' terminals.

watch : Periodically executes a program, displaying output fullscreen.

wc : Counts lines, words, bytes, and characters in files.

wget : Downloads files from a server, can run in background without user login.

whatis : Retrieves a one‑line description from a manual page.

which : Locates the executable associated with a given command by searching the PATH.

while : Repeats a set of commands as long as a command returns true.

who : Provides information about currently logged‑in users.

whoami : Displays the current user's username.

write : Allows communication by copying a line from one user's terminal to another.

X

xargs : Builds and executes commands from standard input, converting input into command arguments.

xdg-open : Opens a file or URL in the user's preferred application.

Y

yes : Prints a continuous stream of a given string; defaults to 'y' if no string is provided.

Z

zdiff : Calls diff on gzip‑compressed files.

zdump : Prints the current time in a specified time zone or all zones named on the command line.

zgrep : Searches for a pattern in files, even if they are compressed.

zip : Compression and archiving utility; stores each file in a .zip archive.