Linux Command Summary

Command

Description

Online Query and Help Commands (2)

man

View command help and dictionary; for more complex needs, use info, though it’s less commonly used.

help

View help for built-in Linux commands, such as the cd command.

File and Directory Operations (18)

ls

Stands for list; lists the contents of a directory and their attributes.

cd

Stands for change directory; switches from the current working directory to a specified one.

cp

Stands for copy; copies files or directories.

find

Means to find; used to search for directories and files within them.

mkdir

Stands for make directories; creates a directory.

mv

Stands for move; moves or renames files.

pwd

Stands for print working directory; shows the absolute path of the current working directory.

rename

Used to rename files.

rm

Stands for remove; deletes one or more files or directories.

rmdir

Stands for remove empty directories; deletes empty directories.

touch

Creates a new empty file or changes the timestamp of an existing file.

tree

Displays the contents of a directory in a tree structure.

basename

Displays the file or directory name.

dirname

Displays the path of a file or directory.

chattr

Changes the extended attributes of a file.

lsattr

Views the extended attributes of a file.

file

Displays the type of a file.

md5sum

Calculates and verifies the MD5 checksum of a file.

View Files and Content Processing Commands (21)

cat

Stands for concatenate; used to connect multiple files and print to the screen or redirect to a specified file.

tac

tac is cat spelled backward; the command displays file content in reverse.

more

Displays file content page by page.

less

Displays file content page by page; the opposite usage of more.

head

Displays the head of file content.

tail

Displays the tail of file content.

cut

Splits each line of a file by a specified delimiter and outputs.

split

Splits a file into different segments.

paste

Merges file content by line.

sort

Sorts the text content of a file.

uniq

Removes duplicate lines.

wc

Counts the number of lines, words, or bytes in a file.

iconv

Converts the encoding format of a file.

dos2unix

Converts DOS format files to UNIX format.

diff

Stands for difference; compares the differences between files, commonly used for text files.

vimdiff

A command-line visual file comparison tool, commonly used for text files.

rev

Reverses the output of file content.

grep/egrep

Filters strings.

join

Merges two files by matching fields.

tr

Replaces or deletes characters.

vi/vim

Command-line text editor.

File Compression and Decompression Commands (4)

tar

Packs and compresses files.

unzip

Extracts files.

gzip

Gzip compression tool.

zip

Compression tool.

Information Display Commands (11)

uname

Displays information related to the operating system.

hostname

Displays or sets the current system’s hostname.

dmesg

Displays boot information, used for diagnosing system faults.

uptime

Displays system uptime and load.

stat

Displays the status of a file or filesystem.

du

Calculates disk space usage.

df

Reports filesystem disk space usage.

top

Displays real-time system resource usage.

free

Views system memory.

date

Displays and sets system time.

cal

Views calendar and time information.

File Search Commands (4)

which

Finds binary commands by searching the environment variable PATH.

find

Traverses the disk to find files or directories.

whereis

Finds binary commands by searching the environment variable PATH.

locate

Finds commands from the database (/var/lib/mlocate/mlocate.db); uses updatedb to update the database.

User Management Commands (10)

useradd

Adds a user.

usermod

Modifies attributes of an existing user.

userdel

Deletes a user.

groupadd

Adds a user group.

passwd

Modifies user password.

chage

Modifies user password expiration.

id

Views user’s uid, gid, and associated user groups.

su

Switches user identity.

visudo

Special command to edit the /etc/sudoers file.

sudo

Executes commands allowed in the sudoers file as another user (default root).

Basic Network Operation Commands (11)

telnet

Remote login using the TELNET protocol.

ssh

Remote login using the SSH encryption protocol.

scp

Stands for secure copy; used to copy files between different hosts.

wget

Command-line file downloader.

ping

Tests network connectivity between hosts.

route

Displays and sets the routing table of the Linux system.

ifconfig

Views, configures, enables, or disables network interfaces.

ifup

Starts the network card.

ifdown

Stops the network card.

netstat

Views network status.

ss

Views network status.

Deep Network Operation Commands (9)

nmap

Network scanning command.

lsof

Stands for list open files; lists files that are currently opened by the system.

mail

Sends and receives emails.

mutt

Email management command.

nslookup

Interactive command to query Internet DNS servers.

dig

Finds DNS resolution processes.

host

Command to query DNS.

traceroute

Tracks the route of data transmission.

tcpdump

Command-line packet capture tool.

Disk and Filesystem Commands (16)

mount

Mounts a filesystem.

umount

Unmounts a filesystem.

fsck

Checks and repairs the Linux filesystem.

dd

Converts or copies files.

dumpe2fs

Exports ext2/ext3/ext4 filesystem information.

dump

Backup tool for ext2/3/4 filesystems.

fdisk

Disk partition command, suitable for partitions under 2TB.

parted

Disk partition command, no disk size limit, commonly used for partitions under 2TB.

mkfs

Formats and creates a Linux filesystem.

partprobe

Updates the kernel’s disk partition table information.

e2fsck

Checks ext2/ext3/ext4 type filesystems.

mkswap

Creates a Linux swap partition.

swapon

Enables the swap partition.

swapoff

Disables the swap partition.

sync

Writes data from memory buffers to disk.

resize2fs

Resizes ext2/ext3/ext4 filesystem.

System Permissions and User Authorization Commands (4)

chmod

Changes file or directory permissions.

chown

Changes the owner and group of a file or directory.

chgrp

Changes the user group of a file.

umask

Displays or sets the permission mask.

View System User Login Information Commands (7)

whoami

Displays the current effective user name, equivalent to executing id -un.

who

Displays information about users currently logged into the system.

w

Displays a list of users logged into the system and the commands they are executing.

last

Displays users who logged into the system.

lastlog

Displays the last login information of all users in the system.

users

Displays a list of all users currently logged into the system.

finger

Finds and displays user information.

Built-in Commands and Others (19)

echo

Prints variables or directly outputs specified strings.

printf

Formats output results to standard output.

rpm

Command to manage rpm packages.

yum

Automates and simplifies the management of rpm packages.

watch

Periodically executes a given command and displays the output in full screen.

alias

Sets a system alias.

unalias

Removes a system alias.

date

Views or sets system time.

clear

Clears the screen.

history

Views the history of executed commands.

eject

Ejects the CD drive.

time

Calculates the execution time of commands.

nc

Powerful networking tool.

xargs

Converts standard input into command line arguments.

exec

Calls and executes commands.

export

Sets or displays environment variables.

unset

Removes variables or functions.

type

Determines whether another command is a built-in command.

bc

Command-line scientific calculator.

System Management and Performance Monitoring Commands (9)

chkconfig

Manages Linux system startup items.

vmstat

Virtual memory statistics.

mpstat

Displays statistics for each available CPU.

iostat

Statistics for system IO.

sar

Comprehensively obtains performance data for CPU, run queues, disk I/O, paging (swap), memory, CPU interrupts, and networking.

ipcs

Reports the status of inter-process communication facilities in Linux; displays information including message lists, shared memory, and semaphore information.

ipcrm

Deletes one or more message queues, semaphore sets, or shared memory identifiers.

strace

Diagnoses and debugs Linux user space tracing. It monitors the interaction between user space processes and the kernel, such as system calls, signal delivery, and process state changes.

ltrace

Tracks library function calls of processes; shows which library functions are called.

Shutdown / Restart / Logout and View System Information Commands (6)

shutdown

Shuts down the system.

halt

Shuts down the system.

poweroff

Turns off the power.

logout

Logs out of the current shell.

exit

Exits the current shell.

Ctrl+d

Shortcut key to exit the current shell.

Process Management Related Commands (15)

bg

Resumes a command that has been paused in the background (executes in the background).

fg

Brings a command from the background to the foreground to continue running.

jobs

Views how many commands are currently running in the background.

kill

Terminates a process.

killall

Terminates processes by their name.

pkill

Terminates processes by their name.

crontab

Command for scheduled tasks.

ps

Displays a snapshot of processes.

pstree

Displays processes in a tree structure.

nice/renice

Adjusts the priority of program execution.

nohup

Runs a specified command ignoring hangup signals.

pgrep

Finds processes matching conditions.

runlevel

Views the current run level of the system.

init

Switches run levels.

service

Starts, stops, restarts, and shuts down system services, and can display the current status of all system services.