Master Essential Linux Commands: A Complete Cheat‑Sheet for System Operations

Online query and help commands (2)

man : View command help and dictionary; more complex information via info (rarely used).

help : Show built‑in Linux command help, e.g., cd.

File and directory operation commands (18)

ls : List directory contents and attribute information.

cd : Change the current working directory to a specified directory.

cp : Copy files or directories.

find : Search for directories and files.

mkdir : Create directories.

mv : Move or rename files.

pwd : Print the absolute path of the current working directory.

rename : Rename files.

rm : Remove one or more files or directories.

rmdir : Remove empty directories.

touch : Create a new empty file or change the timestamp of an existing file.

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

basename : Show the file name or directory name.

dirname : Show the path of a file or directory.

chattr : Change a file’s extended attributes.

lsattr : View a file’s extended attributes.

file : Display the type of a file.

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

File viewing and content processing commands (21)

cat : Concatenate files and print to standard output or redirect to a file.

tac : Reverse the order of cat, displaying 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 specified delimiter and output the fields.

split : Divide a file into smaller pieces.

paste : Merge lines of files side by side.

sort : Sort the textual content of a file.

uniq : Remove duplicate lines.

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

iconv : Convert a file’s character encoding.

dos2unix : Convert DOS‑format files to UNIX format.

diff : Compare differences between files (commonly text files).

vimdiff : Visual file comparison tool in the terminal.

rev : Output file contents in reverse order.

grep/egrep : Filter strings (the third sword of the “three‑sword” trio).

join : Merge two files on common fields.

tr : Replace or delete characters.

vi/vim : Command‑line text editor.

File compression and extraction commands (4)

tar : Archive and compress files.

unzip : Decompress files.

gzip : Gzip compression tool.

zip : Zip compression tool.

Information display commands (11)

uname : Show operating‑system related information.

hostname : Show or set the system’s host name.

dmesg : Display boot messages for diagnosing system faults.

uptime : Show system uptime and load.

stat : Show status of a file or filesystem.

du : Estimate disk space usage.

df : Report filesystem disk space usage.

top : Real‑time display of system resource usage.

free : Show system memory usage.

date : Display or set system time.

cal : View calendar and related time information.

File search commands (4)

which : Locate binary commands by searching the PATH environment.

find : Traverse the disk to locate files or directories.

whereis : Locate binary commands by searching the PATH environment.

locate : Search a database ( /var/lib/mlocate/mlocate.db) for files; update with updatedb.

User management commands (10)

useradd : Add a user.

usermod : Modify existing user attributes.

userdel : Delete a user.

groupadd : Add a user group.

passwd : Change a user’s password.

chage : Modify password expiration.

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

su : Switch user identity.

visudo : Edit the /etc/sudoers file safely.

sudo : Execute commands as another user (default root) as permitted in sudoers.

Basic network operation commands (11)

telnet : Remote login using the TELNET protocol.

ssh : Remote login using the encrypted SSH protocol.

scp : Secure copy files between hosts.

wget : Download files from the command line.

ping : Test network connectivity between hosts.

route : Show or set the Linux routing table.

ifconfig : View, configure, enable, or disable network interfaces.

ifup : Bring a network interface up.

ifdown : Bring a network interface down.

netstat : Show network status.

ss : Show network status.

Advanced network operation commands (9)

nmap : Network scanning tool.

lsof : List open files in the system.

mail : Send and receive email.

mutt : Email management command.

nslookup : Interactive DNS query tool.

dig : Query DNS resolution process.

host : DNS query command.

traceroute : Trace the route packets take to a destination.

tcpdump : Command‑line packet capture tool.

Disk and filesystem commands (16)

mount : Mount a filesystem.

umount : Unmount a filesystem.

fsck : Check and repair Linux filesystems.

dd : Convert or copy files.

dumpe2fs : Export ext2/ext3/ext4 filesystem information.

dump : Backup tool for ext2/3/4 filesystems.

fdisk : Disk partitioning (for disks < 2 TB).

parted : Disk partitioning without size limit (commonly for <2 TB).

mkfs : Format and create a Linux filesystem.

partprobe : Update kernel partition table information.

e2fsck : Check ext2/ext3/ext4 filesystems.

mkswap : Create a Linux swap partition.

swapon : Enable a swap partition.

swapoff : Disable a swap partition.

sync : Flush buffered data to disk.

resize2fs : Resize ext2/ext3/ext4 filesystems.

System permission and user authorization commands (4)

chmod : Change file or directory permissions.

chown : Change file or directory owner and group.

chgrp : Change a file’s group.

umask : Show or set the permission mask.

System user login information commands (7)

whoami : Show the effective user name (same as id -un).

who : Show currently logged‑in users.

w : Show logged‑in users and their running commands.

last : Display recent logins.

lastlog : Show the most recent login for all users.

users : List all users currently logged in.

finger : Look up and display user information.

System management and performance monitoring commands (9)

chkconfig : Manage Linux startup services.

vmstat : Virtual memory statistics.

mpstat : Show per‑CPU statistics.

iostat : Report system I/O statistics.

sar : Collect comprehensive performance data (CPU, queues, I/O, memory, interrupts, network, etc.).

ipcs : Report status of inter‑process communication facilities.

ipcrm : Remove message queues, semaphore sets, or shared memory identifiers.

strace : Trace system calls, signals, and process state changes.

ltrace : Trace library function calls of a process.

Shutdown / reboot / logout and system info commands (6)

shutdown : Shut down the system.

halt : Halt the system.

poweroff : Power off the system.

logout : Exit the current shell session.

exit : Exit the current shell session.

Ctrl+d : Shortcut to exit the current shell.

Process management commands (15)

bg : Resume a paused background job.

fg : Bring a background job to the foreground.

jobs : List current background jobs.

kill : Terminate a process.

killall : Terminate processes by name.

pkill : Terminate processes by name.

crontab : Schedule recurring tasks.

ps : Show a snapshot of processes.

pstree : Display processes in a tree format.

nice/renice : Adjust process priority.

nohup : Run a command immune to hang‑up signals.

pgrep : Find processes matching criteria.

runlevel : Show the current system runlevel.

init : Change the system runlevel.

service : Start, stop, restart, or query the status of system services.