Linux Basic & Advance Commands

Linux Basic Commands

🐧 Basic Linux Commands Cheat Sheet

📍 Navigation & Directory Commands

Command	Example	Explanation
pwd	pwd	Shows the current working directory path.
ls	ls	Lists files and directories in the current location.
ls -la	ls -la	Lists all files including hidden ones, with detailed info like permissions and size.
mkdir	mkdir projects	Creates a new directory named projects.
cd	cd projects	Moves into the specified directory.
cd ..	cd ..	Moves one level up (to parent directory).
cd ~	cd ~	Takes you to your home directory.
cd /	cd /	Takes you to the root directory.

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📁 File & Directory Operations

Command	Example	Explanation
rm	rm file.txt	Deletes a file.
rm -rf	rm -rf folder	Deletes folder and its contents recursively, forcefully. Dangerous — no confirmation!
mv	mv old.txt new.txt	Renames a file. Also used to move files.
cp	cp file1.txt /tmp/	Copies a file to another location.
cp -r	cp -r folder /backup/	Copies a directory recursively.

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🔐 Ownership & Permission Commands

Command	Example	Explanation
chown	chown user:group file.txt	Changes ownership of file or directory.
chmod	chmod 755 script.sh	Changes permissions of a file or directory. 755 = owner full access, others read/execute.

Permission Basics

Symbol	Meaning
r	read
w	write
x	execute
u	user/owner
g	group
o	others
a	all

Example: chmod u+x script.sh

Adds execute permission for the owner.

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📄 Viewing & Editing Files

Command	Example	Explanation
cat	cat file.txt	Displays the contents of file.txt on the terminal.
gedit filename	gedit notes.txt	Opens GUI text editor (for desktop Linux).
vi filename	vi notes.txt	Opens file in vi editor. Press i to insert text, :wq to save & exit.
nano filename	nano notes.txt	Opens file in nano editor (easy CLI editor).

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🛠️ Extra Useful Commands

Command	Example	Explanation
touch	touch index.html	Creates an empty file.
clear	clear	Clears the terminal screen.
history	history	Shows the list of previously used commands.
whoami	whoami	Prints the current logged-in username.

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⚡ Advanced Linux Commands Cheat Sheet

🧰 System Services & Daemon Management (systemctl)

Command	Example	Explanation
systemctl status	systemctl status nginx	Shows the running status of a service.
systemctl start	systemctl start nginx	Starts a service.
systemctl stop	systemctl stop nginx	Stops a service.
systemctl restart	systemctl restart nginx	Restarts a service.
systemctl enable	systemctl enable nginx	Enables service to start on boot.
systemctl disable	systemctl disable nginx	Disables service from starting automatically.
systemctl is-active	systemctl is-active nginx	Checks if a service is currently running.

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📜 Logs & Monitoring

Command	Example	Explanation
cat	cat /var/log/syslog	Prints entire file content to terminal (use with caution for large logs).
tail	tail /var/log/syslog	Shows the last 10 lines of a log file.
tail -f	tail -f /var/log/syslog	Streams the log live (useful for debugging).
head	head file.txt	Shows the first 10 lines of a file.
journalctl	journalctl -u nginx	Shows logs of a systemd service like nginx.
dmesg	dmesg	Displays kernel messages, often used for hardware/debug info.

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🔍 Searching & Filtering (grep)

Command	Example	Explanation
grep	grep "error" syslog	Finds lines containing the word error.
grep -i	grep -i "error" syslog	Case-insensitive search.
grep -r	grep -r "password" /etc	Recursively search directories.
grep -n	grep -n "http" access.log	Shows line numbers for matches.
grep -v	grep -v "debug" syslog	Shows lines not containing the pattern.

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⚙️ Process Management

Command	Example	Explanation
ps	ps aux	Lists all running processes.
top	top	Real-time view of CPU & memory usage.
htop	htop	Enhanced version of top (if installed).
kill	kill 1234	Kills process with PID 1234.
kill -9	kill -9 1234	Force kill a process (immediate termination).
pgrep	pgrep nginx	Finds PID of a process by name.

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🌐 Networking Commands

Command	Example	Explanation
ifconfig / ip a	ip a	Shows network interfaces and IP addresses.
ping	ping google.com	Tests network connectivity to a host.
curl	curl https://example.com	Fetches data from a URL.
wget	wget https://file.com/app.zip	Downloads files from the internet.
netstat -tulnp	netstat -tulnp	Shows listening ports and services.
ss -tulnp	ss -tulnp	Modern replacement for netstat.

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🧱 Disk & File System Commands

Command	Example	Explanation
df -h	df -h	Shows disk usage in human-readable format (GB/MB).
du -sh	du -sh /var/log	Shows size of a directory.
mount	mount /dev/sdb1 /data	Mounts a disk/device.
fdisk	fdisk -l	Lists disk partitions.

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🏁 System Information

Command	Explanation
uname -a	Shows kernel and OS details.
uptime	Shows how long the system is running.
hostname	Prints system hostname.
free -h	Memory usage in human-readable format.

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