Linux Commands

This guide presents the most essential Linux commands you’ll use for everyday tasks, organized by category.

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File and Directory Management

Command	Description	Example Usage
ls	List directory contents	ls -l
cd	Change current directory	cd /path/to/dir
pwd	Show current directory	pwd
mkdir	Make new directory	mkdir new_folder
rmdir	Remove empty directory	rmdir old_folder
rm	Remove file/directory	rm file.txt rm -r dir
cp	Copy files/directories	cp source dest
mv	Move or rename files/directories	mv old_name new_name
touch	Create an empty file	touch file.txt
cat	Display file contents	cat file.txt
nano/vim	Edit files in terminal	nano file.txt vim file.txt

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System and User Management

Command	Description	Example Usage
sudo	Run commands as superuser	sudo apt update
passwd	Change user password	passwd
adduser	Add a new user	sudo adduser username
deluser	Delete a user	sudo deluser username
chown	Change file/directory owner	sudo chown user file.txt
chmod	Change file permissions	chmod 755 script.sh
id	Show user identity	id
groups	Show group memberships	groups

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Package Management (Ubuntu/Debian)

Command	Description	Example Usage
apt update	Update package index	sudo apt update
apt upgrade	Upgrade installed packages	sudo apt upgrade
apt install	Install a package	sudo apt install curl
apt remove	Remove a package	sudo apt remove nginx
apt search	Search for a package	apt search nginx

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Disk and Process Management

Command	Description	Example Usage
df -h	Show disk usage	df -h
du -sh	Show directory/file size	du -sh /home/user
top	Monitor system processes	top
htop	Advanced process viewer	htop
ps aux	List running processes	ps aux
kill	Kill a process by PID	kill 12345
killall	Kill all processes by name	killall firefox
free -h	Show memory usage	free -h

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Networking

Command	Description	Example Usage
ping	Test network connectivity	ping example.com
ip a	Show network interfaces	ip a
netstat -tuln	Show open/listening ports	netstat -tuln
ss -ltn	Show listening TCP ports	ss -ltn
lsof -i -P -n	List all open network connections	lsof -i -P -n
lsof -i :80	Show processes using port 80	lsof -i :80
ssh	SSH to a remote machine	ssh user@host
scp	Copy files over SSH	scp file.txt user@host:/path/
wget	Download files from internet	wget http://example.com/file
curl	Download or transfer data	curl -O http://url/file

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Text Processing

Command	Description	Example Usage
grep	Search text patterns	grep "error" logfile.txt
awk	Pattern scanning/processing	awk '{print $1}' file.txt
sed	Stream editor for text	sed 's/old/new/g' file.txt
sort	Sort lines of text files	sort names.txt
head/tail	Show start/end of files	head -10 file.txt, tail -20 file

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Miscellaneous

Command	Description	Example Usage
echo	Print text to terminal	echo "Hello"
history	Show command history	history
clear	Clear terminal screen	clear
shutdown	Shutdown system	sudo shutdown now
reboot	Reboot system	sudo reboot
date	Show date and time	date
uname -a	Show system information	uname -a
man	Manual/help for a command	man ls
--help	Show command help	ls --help

Service Management Commands in Linux

The following table provides commonly used service management commands in Linux, particularly with systemd and service.

Action	systemctl Command	service Command
Start a service	systemctl start <service>	service <service> start
Stop a service	systemctl stop <service>	service <service> stop
Restart a service	systemctl restart <service>	service <service> restart
Reload a service	systemctl reload <service>	service <service> reload
Enable at boot	systemctl enable <service>	chkconfig <service> on
Disable at boot	systemctl disable <service>	chkconfig <service> off
Check status	systemctl status <service>	service <service> status
Show all services	systemctl list-units --type=service	service --status-all
Check if enabled	systemctl is-enabled <service>	chkconfig --list <service>
Mask a service	systemctl mask <service>	(Not available in service)
Unmask a service	systemctl unmask <service>	(Not available in service)
Reboot system	systemctl reboot	reboot
Shutdown system	systemctl poweroff	shutdown now
View logs	journalctl -u <service> -f	(Check /var/log/syslog or others)

🔹 Replace <service> with the actual service name (e.g., nginx, ssh, docker).

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