Essential Linux Commands

Use at your own risk. All guides and scripts are provided for educational purposes only. Always review and understand any code before running it — especially with administrative privileges. Test in a safe environment before using in production. Your system, your responsibility.

This is a practical reference for the Linux commands you will actually use day to day. Not an exhaustive list — just the ones that matter most when working with servers, home labs, and infrastructure.

Navigation

Command	What it does
`pwd`	Print current directory
`ls`	List files and folders
`ls -la`	List all files with details and hidden files
`cd /path/to/folder`	Change directory
`cd ..`	Go up one level
`cd ~`	Go to home directory
`cd -`	Go back to previous directory

# Example
ls -la /etc/

Files and Directories

Command	What it does
`mkdir foldername`	Create a directory
`mkdir -p a/b/c`	Create nested directories
`touch file.txt`	Create an empty file
`cp file.txt /destination/`	Copy a file
`cp -r folder/ /destination/`	Copy a folder recursively
`mv file.txt /destination/`	Move or rename a file
`rm file.txt`	Delete a file
`rm -rf folder/`	Delete a folder and all contents
`cat file.txt`	Print file contents
`less file.txt`	Scroll through file contents
`head -n 20 file.txt`	Show first 20 lines
`tail -n 20 file.txt`	Show last 20 lines
`tail -f file.txt`	Follow file in real time (great for logs)

rm -rf deletes files and folders permanently with no confirmation. Double-check your path before running it.

Searching

Command	What it does
`grep "text" file.txt`	Search for text in a file
`grep -r "text" /path/`	Search recursively in a directory
`grep -i "text" file.txt`	Case-insensitive search
`find /path -name "*.log"`	Find files by name
`find /path -type f -mtime -7`	Find files modified in last 7 days

# Find all .conf files under /etc
find /etc -name "*.conf"

# Search for "error" in all log files
grep -r "error" /var/log/

Permissions

Command	What it does
`chmod 755 file`	Set permissions (rwxr-xr-x)
`chmod +x script.sh`	Make a file executable
`chown user:group file`	Change owner and group
`chown -R user:group folder/`	Change ownership recursively
`ls -l`	View file permissions

Permission numbers explained:

7 = rwx (read, write, execute)
6 = rw- (read, write)
5 = r-x (read, execute)
4 = r-- (read only)
0 = --- (no permissions)

# Make a script executable
chmod +x deploy.sh

# Give owner full access, others read only
chmod 644 config.txt

System Information

Command	What it does
`uname -a`	Kernel and system info
`hostname`	Show hostname
`uptime`	How long the system has been running
`whoami`	Current logged-in user
`df -h`	Disk usage (human readable)
`du -sh /path/`	Size of a specific folder
`free -h`	RAM usage
`top`	Real-time process monitor
`htop`	Better process monitor (install with apt)
`lscpu`	CPU information
`lsblk`	List block devices (disks)

Process Management

Command	What it does
`ps aux`	List all running processes
`ps aux	grep nginx`
`kill PID`	Stop a process by ID
`kill -9 PID`	Force kill a process
`pkill nginx`	Kill process by name

# Find and kill a stuck process
ps aux | grep myapp
kill -9 12345

Services (systemd)

Command	What it does
`sudo systemctl status nginx`	Check service status
`sudo systemctl start nginx`	Start a service
`sudo systemctl stop nginx`	Stop a service
`sudo systemctl restart nginx`	Restart a service
`sudo systemctl enable nginx`	Start service on boot
`sudo systemctl disable nginx`	Disable service on boot
`sudo journalctl -u nginx -f`	Follow service logs live

Networking

Command	What it does
`ip a`	Show IP addresses and interfaces
`ip r`	Show routing table
`ping google.com`	Test connectivity
`curl https://example.com`	Fetch a URL
`wget https://example.com/file`	Download a file
`ss -tulnp`	Show open ports and listening services
`nmap -sV 192.168.1.1`	Scan a host (install nmap first)
`traceroute google.com`	Trace network path

# Check what is listening on port 80
ss -tulnp | grep :80

Package Management (apt)

Command	What it does
`sudo apt update`	Update package lists
`sudo apt upgrade`	Upgrade installed packages
`sudo apt install nginx`	Install a package
`sudo apt remove nginx`	Remove a package
`sudo apt autoremove`	Remove unused dependencies
`apt search nginx`	Search for a package
`apt show nginx`	Show package details

Text Editing

Command	What it does
`nano file.txt`	Open file in nano editor
`vim file.txt`	Open file in vim editor

nano basics:

CTRL+O — save
CTRL+X — exit
CTRL+W — search

vim basics:

i — enter insert mode
ESC — exit insert mode
:w — save
:q — quit
:wq — save and quit
:q! — quit without saving

Useful Shortcuts

Shortcut	What it does
`CTRL+C`	Cancel current command
`CTRL+Z`	Suspend current process
`CTRL+L`	Clear the terminal
`CTRL+A`	Jump to beginning of line
`CTRL+E`	Jump to end of line
`↑ / ↓`	Navigate command history
`!!`	Repeat last command
`sudo !!`	Repeat last command with sudo