Linux

Use case: cd <directory>
Example: To change to the “Downloads” directory

cd Downloads

Use case: ls [options] [directory]
Example: To list files with detailed information

ls -l

Use case: cp [options] source destination
Example: To copy a file to another directory

cp file.txt /path/to/destination/

Use case: mv [options] source destination
Example: To move a file to another directory

mv file.txt /path/to/destination/

Use case: rm [options] file/directory
Example: To remove a file

rm file.txt

Use case: mkdir [options] directory
Example: To create a directory named “new_folder”

mkdir new_folder

Use case: find [directory] -name [filename]
Example: To find all .txt files in the current directory

find . -name "*.txt"

Use case: cat [filename]
Example: To display the content of a file

cat file.txt

Use case: nano [filename]
Example: To edit a file using nano

nano file.txt

Use case: top
Example: To view and manage running processes

top

Use case: netstat [options]
Example: To display all active network connections

netstat -a

Use case: ufw [options]
Example: To enable the firewall

ufw enable

Use case: useradd [options] username
Example: To add a new user named “john”

useradd john

Use case: passwd [username]
Example: To change the password for the user “john”

passwd john

Use case: chmod [options] permissions file
Example: To give read and write permissions to a file

chmod +rw file.txt

Use case: tar [options] archive_name files/directories
Example: To create a compressed archive named “backup.tar.gz” of the “Documents” directory

tar -czvf backup.tar.gz Documents/

Use case: grep [options] pattern file(s)
Example: To search for the word “error” in all .log files

grep "error" *.log

Use case: scp [options] source destination
Example: To copy a local file to a remote server

scp file.txt user@remote:/path/to/destination/

Use case: ps [options]
Example: To display information about all processes

ps aux

Use case: uname [options]
Example: To display the system name and version

uname -a

Use case: tcpdump [options] [expression]
Example: To capture packets on interface eth0

tcpdump -i eth0

Use case: cryptsetup [options] command
Example: To create an encrypted volume

cryptsetup luksFormat /dev/sdb1

Use case: nice [options] command
Example: To run a command with a lower priority

nice -n 10 command

Use case: sha256sum [options] file(s)
Example: To calculate the SHA256 hash of a file

sha256sum file.txt

Use case: ssh-keygen [options]
Example: To generate an SSH key pair

ssh-keygen -t rsa -b 2048

Use case: quota [options]
Example: To display disk quotas for the current user

quota -v

Use case: shred [options] file(s)
Example: To securely delete a file

shred -u file.txt

Use case: du [options] [directory]
Example: To display disk usage for the current directory

du -h

Use case: fsck [options] [filesystem]
Example: To check and repair the root file system

fsck /

Use case: nmap [options] target
Example: To scan open ports on a target

nmap -p 1-1000 target

Use case: fdisk [options] device
Example: To create a new partition on /dev/sdb

fdisk /dev/sdb

Use case: chown [options] owner:group file(s)
Example: To change the owner of a file to user “john”

chown john: file.txt

Use case: iftop
Example: To monitor network connections in real-time

iftop

Use case: gpg [options] file
Example: To encrypt a file with GPG

gpg -c file.txt

Use case: mount [options] device directory
Example: To mount a USB drive to /mnt/usb

mount /dev/sdc1 /mnt/usb

Use case: journalctl [options]
Example: To view system logs

journalctl

Use case: ifconfig [interface] [options]
Example: To display network interfaces

ifconfig

Use case: kill [options] PID
Example: To kill a process with PID 1234

kill 1234

Use case: htop
Example: To interactively view and manage system processes

htop

Use case: ip [options] [object]
Example: To display IP addresses and routing information

ip address show

Use case: mkfs [options] device
Example: To create an ext4 file system on /dev/sdb1

mkfs.ext4 /dev/sdb1

Use case: wireshark [options] [filename]
Example: To capture and analyze network packets

wireshark

Use case: sudo nano /etc/ssh/sshd_config
Example: To edit the SSH server configuration file

sudo nano /etc/ssh/sshd_config

Use case: last [options] [username]
Example: To display last logged-in users

last

Use case: free [options]
Example: To display memory usage statistics

free -m

Use case: md5sum [options] file(s)
Example: To calculate the MD5 hash of a file

md5sum file.txt

Use case: sudo apt update && sudo apt upgrade
Example: To update the package list and upgrade installed packages

sudo apt update && sudo apt upgrade

Use case: uptime
Example: To display system uptime

uptime

Use case: vim [filename]
Example: To edit a file using vim

vim file.txt

Use case: sudo shutdown [options] [time]
Example: To shutdown the system immediately

sudo shutdown now