1. File and Directory Navigation

Command	Description	Example
pwd	Displays the current working directory.	pwd → /home/user/Documents
ls	Lists files and directories in the current location.	ls
ls -l	Lists files with detailed info (permissions, size, date, owner).	ls -l
cd [directory]	Changes the current directory.	cd /etc
cd ..	Moves up one level in the directory structure.	cd ..
cd /	Goes to the root directory.	cd /

2. File Management

Command	Description	Example
touch [file]	Creates an empty file.	touch notes.txt
cp [source] [destination]	Copies files or directories.	cp file.txt /backup/
mv [source] [destination]	Moves or renames files/directories.	mv old.txt new.txt
rm [file]	Deletes a file.	rm temp.txt
rm -r [directory]	Deletes a directory and all its contents.	rm -r old_folder/

3. Text Manipulation

Command	Description	Example
cat [file]	Displays the content of a file.	cat readme.txt
less [file]	Opens a file for paginated viewing (scroll up/down).	less /etc/passwd
head [file]	Shows the first 10 lines.	head log.txt
tail [file]	Shows the last 10 lines.	tail log.txt
grep "text" [file]	Searches for a specific word or phrase inside a file.	grep "error" log.txt

4. Permissions and Ownership

Command	Description	Example
chmod [permissions] [file]	Changes file permissions using numeric or symbolic mode.	chmod 755 script.sh
chown [user:group] [file]	Changes file owner and group.	chown root:root config.txt

5. Process Management

Command	Description	Example
ps	Displays running processes.	ps aux
top	Real-time view of system processes and usage.	top
kill [PID]	Terminates a process by its ID.	kill 1234
killall [name]	Kills all processes with a given name.	killall firefox

6. User and Group Management

Command	Description	Example
whoami	Displays the current logged-in user.	whoami
who	Lists all users currently connected.	who
adduser [user]	Creates a new user account.	sudo adduser alice
deluser [user]	Deletes a user account.	sudo deluser bob
passwd [user]	Changes a user’s password.	sudo passwd alice

7. Networking

Command	Description	Example
ping [host]	Tests network connectivity.	ping google.com
ifconfig / ip a	Shows network interfaces and IP addresses.	ip a
netstat -tulnp	Displays open ports and listening services.	sudo netstat -tulnp
wget [URL]	Downloads a file from the web.	wget https://example.com/file.zip
curl [URL]	Displays or transfers data from a URL.	curl https://api.github.com

8. Package Management

-Debian / Ubuntu (APT)

Command	Description	Example
apt update	Updates the package list.	sudo apt update
apt upgrade	Upgrades all installed packages.	sudo apt upgrade
apt install [package]	Installs a package.	sudo apt install vim
apt remove [package]	Removes a package.	sudo apt remove nano

–RedHat / CentOS (YUM)

Command	Description	Example
yum update	Updates packages.	sudo yum update
yum install [package]	Installs a package.	sudo yum install git
yum remove [package]	Removes a package.	sudo yum remove httpd

9. Compression and Archiving

Command	Description	Example
tar -cvf file.tar [files]	Creates a tar archive.	tar -cvf backup.tar /home/user/
tar -xvf file.tar	Extracts a tar archive.	tar -xvf backup.tar
gzip [file]	Compresses a file using gzip.	gzip notes.txt
gunzip [file.gz]	Decompresses a gzip file.	gunzip notes.txt.gz
zip [file.zip] [files]	Creates a ZIP file.	zip archive.zip *.txt
unzip [file.zip]	Extracts a ZIP archive.	unzip archive.zip

10. Other Useful Utilities

Command	Description	Example
clear	Clears the terminal screen.	clear
history	Shows previously used commands.	history
echo "text"	Displays text or variables.	echo $USER
date	Displays the current date and time.	date
shutdown -h now	Shuts down the system immediately.	sudo shutdown -h now
reboot	Restarts the system.	sudo reboot