Linux · CLI · System Administration · DevOps

Linux Commands
Cheatsheet

A comprehensive quick reference for essential Linux CLI commands — covering file operations, permissions, processes, networking, text processing, and system info.

OS: Linux / Unix

Shell: bash / sh / zsh

Level: Beginner → Advanced

Sections: 8

GeeksforGeeks Guide

What is the Linux CLI?

The Linux Command Line Interface (CLI) is a text-based interface for interacting with the operating system. Unlike graphical interfaces, the CLI gives you direct control over the system through commands typed in a terminal or shell (typically Bash).

Why use it? The CLI is faster, scriptable, more powerful, and often the only interface available on servers. Remote servers (SSH), containers (Docker), and cloud infrastructure are predominantly managed via CLI.

Real-world use: System administrators, DevOps engineers, security analysts, developers, and penetration testers all rely on Linux CLI daily. It is tested in CompTIA Linux+, RHCSA, and OSCP certifications.

Server administration & DevOps

Security analysis & pentesting

Scripting & automation

Cloud & container management

50+

Commands

1. File Operations

Command	Description	Example
ls	List files and directories	ls -la /etc
ls -la	Long list with hidden files	ls -la ~
cd	Change directory	cd /var/log
pwd	Print current working directory	pwd
cp	Copy file or directory	cp file.txt /tmp/
cp -r	Copy directory recursively	cp -r dir/ /backup/
mv	Move or rename file/directory	mv old.txt new.txt
rm	Remove file	rm file.txt
rm -rf	Remove directory recursively (⚠️ dangerous)	rm -rf /tmp/junk/
mkdir	Create directory	mkdir -p /opt/app/logs
touch	Create empty file / update timestamp	touch newfile.txt
find	Search files by name, type, size	find / -name "*.conf" 2>/dev/null
locate	Fast file search using database	locate passwd
ln -s	Create symbolic (soft) link	ln -s /etc/nginx nginx_conf
du -sh	Disk usage of file/directory	du -sh /var/log/
df -h	Disk free space (all mounts)	df -h
stat	File metadata (size, inode, timestamps)	stat /etc/passwd
file	Identify file type	file suspicious.bin

2. File Viewing & Text Processing

Command	Description	Example
cat	Display file contents	cat /etc/hosts
less	Scrollable file viewer	less /var/log/syslog
head	First N lines of file	head -20 access.log
tail	Last N lines; -f to follow live	tail -f /var/log/auth.log
grep	Search text with pattern	grep -r "error" /var/log/
grep -i	Case-insensitive search	grep -i "fail" auth.log
grep -n	Show line numbers	grep -n "root" /etc/passwd
awk	Pattern scanning & text processing	awk '{print $1}' access.log
sed	Stream editor for text substitution	sed 's/foo/bar/g' file.txt
sort	Sort lines alphabetically/numerically	sort -n numbers.txt
uniq	Remove duplicate adjacent lines	sort ips.txt \| uniq -c
cut	Extract columns from text	cut -d: -f1 /etc/passwd
wc	Word/line/byte count	wc -l access.log
diff	Compare two files line by line	diff file1.txt file2.txt
echo	Print text to stdout	echo "Hello" >> log.txt
tee	Read stdin and write to file + stdout	ls \| tee output.txt
xargs	Build command from stdin	find . -name "*.log" \| xargs rm

3. Permissions & Ownership

Command	Description	Example
chmod	Change file permissions	chmod 755 script.sh
chmod +x	Add execute permission	chmod +x deploy.sh
chown	Change file owner	chown www-data:www-data /var/www/
chgrp	Change group ownership	chgrp devs project/
umask	Set default permission mask	umask 022
getfacl	Get file ACL	getfacl /etc/passwd
setfacl	Set file ACL	setfacl -m u:alice:rwx file
sudo	Execute as superuser	sudo systemctl restart nginx
su	Switch user	su - alice
id	Show current user UID/GID/groups	id
whoami	Print current username	whoami
groups	List groups current user belongs to	groups

# Permission notation: rwxrwxrwx → owner/group/others
# Octal: r=4, w=2, x=1
chmod 644 file.txt    # rw-r--r-- (owner rw, rest read)
chmod 755 script.sh   # rwxr-xr-x (owner rwx, rest rx)
chmod 600 id_rsa      # rw------- (SSH key must be 600)
chmod 777 public/     # rwxrwxrwx (⚠️ avoid in production)

4. Processes & System

Command	Description	Example
ps aux	List all running processes	ps aux \| grep nginx
top	Interactive process monitor	top
htop	Enhanced interactive monitor	htop
kill	Send signal to process by PID	kill -9 1234
killall	Kill all processes by name	killall nginx
pkill	Kill process by name pattern	pkill -f "python app.py"
jobs	List background jobs	jobs
bg / fg	Background / foreground a job	bg %1
nohup	Run process immune to hangup	nohup ./server &
systemctl	Control systemd services	sudo systemctl start ssh
service	Control SysV services	sudo service apache2 restart
crontab -e	Edit scheduled cron jobs	crontab -e
free -h	Memory usage (human-readable)	free -h
uptime	System uptime and load avg	uptime
uname -a	Kernel and OS information	uname -a
lsof	List open files and sockets	lsof -i :80

5. Networking

Command	Description	Example
ip addr	Show IP addresses (modern)	ip addr show eth0
ifconfig	Show/configure interfaces (legacy)	ifconfig -a
ping	Test host reachability	ping -c 4 8.8.8.8
traceroute	Trace packet route to host	traceroute google.com
netstat -tlnp	Listening ports (legacy)	netstat -tlnp
ss -tlnp	Listening ports (modern)	ss -tlnp
dig	DNS lookup (detailed)	dig +short google.com
nslookup	DNS lookup (interactive)	nslookup google.com
curl	Transfer data from URL	curl -I https://example.com
wget	Download file from URL	wget https://example.com/file.zip
ssh	Secure Shell remote login	ssh [email protected]
scp	Secure copy over SSH	scp file.txt user@host:/tmp/
nc	Netcat — TCP/UDP connections	nc -lvnp 4444
iptables -L	List firewall rules	sudo iptables -L -n -v
hostname	Show or set hostname	hostname -I

6. Package Management

# Debian / Ubuntu (apt)
sudo apt update                  # refresh package index
sudo apt upgrade                 # upgrade installed packages
sudo apt install nginx           # install package
sudo apt remove nginx            # remove package
sudo apt purge nginx             # remove + config files
sudo apt autoremove              # remove orphaned deps
apt search nginx                 # search for package
dpkg -l | grep nginx             # check if installed

# Red Hat / CentOS (yum / dnf)
sudo dnf install httpd           # install package
sudo yum update                  # update all packages
rpm -qa | grep nginx             # list installed RPMs

7. Archives & Compression

# tar — tape archive
tar -czf archive.tar.gz dir/     # create gzip archive
tar -xzf archive.tar.gz          # extract gzip archive
tar -cjf archive.tar.bz2 dir/   # create bzip2 archive
tar -tf archive.tar.gz           # list contents without extracting
tar -xzf archive.tar.gz -C /tmp/ # extract to specific dir

# zip / unzip
zip -r backup.zip /var/www/      # create zip
unzip backup.zip -d /tmp/        # extract zip

# gzip / gunzip
gzip large_file.txt              # compress single file
gunzip large_file.txt.gz         # decompress

8. Redirects, Pipes & Shortcuts

# I/O Redirection
command > file.txt               # stdout to file (overwrite)
command >> file.txt              # stdout to file (append)
command 2> errors.txt            # stderr to file
command &> all.txt               # stdout + stderr to file
command < input.txt              # stdin from file

# Pipes
cmd1 | cmd2                      # pipe stdout to next command
ps aux | grep nginx | awk '{print $2}'

# Background / job control
command &                        # run in background
Ctrl+Z                           # suspend current job
Ctrl+C                           # interrupt (kill) current job
Ctrl+D                           # EOF / logout

# Useful shortcuts
!!                               # repeat last command
!$                               # last argument of previous cmd
history | tail -20               # recent command history
Ctrl+R                           # reverse search history
alias ll='ls -la'                # create command alias