Essential Linux Commands: A Complete Reference Guide

Online Query and Help Commands (2)

man : View command help and manual pages; more complex info available via info.

help : Show help for built‑in shell commands such as cd.

File and Directory Operations (18)

ls : List directory contents and attributes.

cd : Change the current working directory.

cp : Copy files or directories.

find : Search for files and directories.

mkdir : Create a new directory.

mv : Move or rename files.

pwd : Print the absolute path of the current directory.

rename : Rename a file.

rm : Remove one or more files or directories.

rmdir : Remove empty directories.

touch : Create an empty file or update a file’s timestamps.

tree : Display directory contents in a tree‑like format.

basename : Show the filename or directory name.

dirname : Show the path of a file or directory.

chattr : Change a file’s extended attributes.

lsattr : List a file’s extended attributes.

file : Determine the file type.

md5sum : Compute and verify a file’s MD5 checksum.

File Viewing and Content Processing (21)

cat : Concatenate files and output to the screen or redirect.

tac : Reverse the output of cat (display file contents backwards).

more : Paginate file output.

less : Paginate file output (inverse of more).

head : Show the beginning of a file.

tail : Show the end of a file.

cut : Split each line of a file by a delimiter and output selected fields.

split : Divide a file into smaller pieces.

paste : Merge lines of files side by side.

sort : Sort text lines in a file.

uniq : Remove duplicate lines.

wc : Count lines, words, or bytes in a file.

iconv : Convert file encoding.

dos2unix : Convert DOS‑format files to UNIX format.

diff : Compare differences between files.

vimdiff : Visual file comparison in the terminal.

rev : Reverse the order of characters in each line.

grep/egrep : Filter text using regular expressions.

join : Join two files on a common field.

tr : Translate or delete characters.

vi/vim : Command‑line text editor.

File Compression and Extraction (4)

tar : Archive files.

unzip : Extract ZIP archives.

gzip : Compress files using gzip.

zip : Create ZIP archives.

Information Display Commands (11)

uname : Show operating‑system information.

hostname : Display or set the system’s hostname.

dmesg : Show kernel boot messages for diagnostics.

uptime : Display system uptime and load average.

stat : Show file or filesystem status.

du : Estimate disk space usage.

df : Report filesystem disk space usage.

top : Real‑time view of system resource usage.

free : Display memory usage.

date : Show or set the system date and time.

cal : Display a calendar.

File Search Commands (4)

which : Locate a binary in the PATH.

find : Search the filesystem for files or directories.

whereis : Locate binary, source, and manual page files.

locate : Find files using a prebuilt database ( updatedb updates it).

User Management Commands (10)

useradd : Add a new user.

usermod : Modify an existing user’s attributes.

userdel : Delete a user.

groupadd : Add a new group.

passwd : Change a user’s password.

chage : Change password expiration information.

id : Show a user’s UID, GID, and group memberships.

su : Switch user identity.

visudo : Safely edit the /etc/sudoers file.

sudo : Execute a command as another user (default root) per sudoers rules.

Basic Network Operations (11)

telnet : Remote login using the TELNET protocol.

ssh : Secure remote login via SSH.

scp : Securely copy files between hosts.

wget : Download files from the command line.

ping : Test network connectivity between hosts.

route : Display or modify the kernel routing table.

ifconfig : View and configure network interfaces.

ifup : Bring a network interface up.

ifdown : Bring a network interface down.

netstat : Show network connections, routing tables, and interface statistics.

ss : Display socket statistics (modern replacement for netstat).

Advanced Network Operations (9)

nmap : Network scanning tool.

lsof : List open files and the processes using them.

mail : Send and receive email.

mutt : Command‑line email client.

nslookup : Interactive DNS query tool.

dig : DNS lookup utility.

host : Simple DNS query command.

traceroute : Trace the route packets take to a network host.

tcpdump : Command‑line packet capture tool.

Disk and Filesystem Commands (16)

mount : Mount a filesystem.

umount : Unmount a filesystem.

fsck : Check and repair a Linux filesystem.

dd : Convert and copy files, often used for low‑level copying.

dumpe2fs : Dump ext2/3/4 filesystem information.

dump : Backup ext2/3/4 filesystems.

fdisk : Partition disks up to 2 TB.

parted : Partition disks without size limits (commonly for <2 TB).

mkfs : Create a filesystem on a partition.

partprobe : Inform the kernel of partition table changes.

e2fsck : Check ext2/3/4 filesystems.

mkswap : Set up a Linux swap area.

swapon : Enable a swap area.

swapoff : Disable a swap area.

sync : Flush filesystem buffers to disk.

resize2fs : Resize ext2/3/4 filesystems.

System Permissions and Authorization (4)

chmod : Change file or directory permissions.

chown : Change file or directory owner and group.

chgrp : Change a file’s group ownership.

umask : Set the default permission mask for newly created files.

System User Login Information (7)

whoami : Show the effective username of the current user.

who : List users currently logged in.

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

last : Display a list of recent logins.

lastlog : Show the most recent login of each user.

users : List usernames of users currently logged in.

finger : Retrieve detailed information about a user.

Built‑in Commands and Others (19)

echo : Print text or variable values to the terminal.

printf : Format and print data.

rpm : Manage RPM packages.

yum : High‑level package manager for RPM‑based systems.

watch : Periodically execute a command and display its output.

alias : Define command aliases.

unalias : Remove command aliases.

date : Show or set the system date and time.

clear : Clear the terminal screen.

history : Show command history.

eject : Eject removable media such as a CD/DVD.

time : Measure the execution time of a command.

nc : Netcat – a versatile networking utility.

xargs : Build and execute command lines from standard input.

exec : Replace the shell with the specified command.

export : Set or display environment variables.

unset : Remove variables or functions.

type : Determine how a command would be interpreted (builtin, file, alias).

bc : Command‑line calculator.

System Management and Performance Monitoring (9)

<img src="https://mmbiz.qpic.cn/mmbiz_png/b96CibCt70iaajvl7fD4ZCicMcjhXMp1v6UXcBIdyPOYfUfaibicSXbZSrkFL9jwZRTUz8aKA1zXq1GDV8Z7uXeep6w/640" alt=""/>

chkconfig : Manage system services that start at boot.

vmstat : Report virtual memory statistics.

mpstat : Show CPU usage statistics.

iostat : Report CPU and I/O statistics.

sar : Collect, report, and save system activity information.

ipcs : Report inter‑process communication facilities.

ipcrm : Remove IPC objects (message queues, semaphores, shared memory).

strace : Trace system calls and signals.

ltrace : Trace library calls.

Shutdown / Reboot / Logout Commands (6)

shutdown : Power off the system.

halt : Halt the system.

poweroff : Turn off the power.

logout : Exit the current login shell.

exit : Exit the current shell.

Ctrl+d : Shortcut to exit the shell.

Process Management Commands (15)

bg : Resume a suspended job in the background.

fg : Bring a background job to the foreground.

jobs : List current jobs.

kill : Send a signal to terminate a process.

killall : Kill processes by name.

pkill : Kill processes by name using patterns.

crontab : Manage scheduled tasks.

ps : Snapshot of current processes.

pstree : Display processes as a tree.

nice/renice : Adjust process priority.

nohup : Run a command immune to hangup signals.

pgrep : Search for processes matching criteria.

runlevel : Show the current system runlevel.

init : Change the system runlevel.

service : Start, stop, restart, or query system services.