ls

List directories

Example: ls -l

pwd

Print working directory

Example: pwd

cd

Navigate through directories

Example: cd /path/to/directory

mkdir

Create directories

Example: mkdir new_directory

mv

Move or rename files

Example: mv file1 file2

cp

Copy files

Example: cp file1 file2

rm

Delete files or directories

Example: rm file1

touch

Create blank/empty files

Example: touch file.txt

ln

Create symbolic links

Example: ln -s /path/to/target link_name

cat

Display file contents

Example: cat file.txt

clear

Clear the terminal display

Example: clear

echo

Print text

Example: echo "Hello, world!"

less

Display paged outputs

Example: less file.txt

man

Access manual pages

Example: man ls

uname

Get basic information about the OS

Example: uname -a

whoami

Get the active username

Example: whoami

tar

Extract and compress files

Example: tar -xvf file.tar

grep

Search for a string within an output

Example: grep "pattern" file.txt

head

Return the specified number of lines from the top

Example: head -n 10 file.txt

tail

Return the specified number of lines from the bottom

Example: tail -n 10 file.txt

diff

Find the difference between two files

Example: diff file1 file2

cmp

Check if two files are identical

Example: cmp file1 file2

comm

Combine the functionality of diff and cmp

Example: comm file1 file2

sort

Sort the content of a file

Example: sort file.txt

export

Export environment variables

Example: export VARIABLE=value

zip

Zip files

Example: zip archive.zip file1 file2

unzip

Unzip files

Example: unzip archive.zip

ssh

Secure Shell command

Example: ssh user@hostname

service

Start and stop services

Example: service apache2 start

ps

Display active processes

Example: ps aux

kill and killall

Kill active processes by process ID or name

Example: kill PID

Example: killall process_name

df

Display disk filesystem information

Example: df -h

mount

Mount file systems

Example: mount /dev/sdb1 /mnt

chmod

Change file permissions

Example: chmod 755 file.sh

chown

Grant ownership of files or folders

Example: chown user:group file.txt

ifconfig

Display network interfaces and IP addresses

Example: ifconfig

traceroute

Trace all the network hops to reach the destination

Example: traceroute google.com

wget

Direct download files from the internet

Example: wget http://example.com/file.txt

ufw

Firewall command

Example: ufw allow 22/tcp

iptables

Base firewall for all other firewall utilities to interface with

Example: iptables -A INPUT -p tcp --dport 80 -j ACCEPT

apt, pacman, yum, rpm

Package managers depending on the distro

Example: apt-get install package_name

Example: pacman -S package_name

Example: yum install package_name

Example: rpm -i package.rpm

sudo

Escalate privileges in Linux

Example: sudo apt-get update

cal

View a command-line calendar

Example: cal

alias

Create custom shortcuts for regularly used commands

Example: alias ll='ls -l'

dd

Create bootable USB sticks

Example: dd if=image.iso of=/dev/sdX bs=4M

whereis

Locate the binary, source, and manual pages for a command

Example: whereis ls

whatis

Find what a command is used for

Example: whatis ls

top

View active processes live with their system usage

Example: top

useradd and usermod

Add new user or change existing user's data

Example: useradd username

Example: usermod -aG groupname username

passwd

Create or update passwords for existing users

Example: passwd username