🔑 User & Permissions
| # Switch user | su - username |
| # Add new user | sudo adduser newuser |
| # Add user to sudoers | sudo usermod -aG sudo newuser |
| # Change permissions | chmod 755 file.sh |
| # Change ownership | chown user:group file.txt |
📂 File & Directory Management
| # List files (long format, hidden files) | ls -la |
| # Change directory | cd /path/to/dir |
| # Make a new directory | mkdir new_folder |
| # Remove directory (empty) | rmdir old_folder |
| # Copy file | cp file1.txt /path/to/dir/ |
| # Move or rename file | mv oldname.txt newname.txt |
| # Remove file | rm file.txt |
| # Find files by name | find /path -name "*.log" |
📦 Package Management (Ubuntu/Debian)
| # Update package lists | sudo apt update |
| # Upgrade installed packages | sudo apt upgrade |
| # Install a package | sudo apt install package-name |
| # Remove a package | sudo apt remove package-name |
| # Search for a package | apt search package-name |
⚙️ System Information
| # Show current user | whoami |
| # Show system info | uname -a |
| # Show disk usage | df -h |
| # Show memory usage | free -h |
| # Show running processes | ps aux |
| # Show real-time processes | top |
🌐 Networking
| # Show IP address | ip addr show |
| # Ping a host | ping -c 4 google.com |
| # Show listening ports | sudo netstat -tuln |
| # Test open port (e.g., port 22) | nc -zv localhost 22 |
| # Download file with wget | wget http://example.com/file.zip |
🔐 SSH
| # Connect to remote host | ssh user@host |
| # Connect with identity file | ssh -i ~/.ssh/id_rsa user@host |
| # Copy file to remote | scp file.txt user@host:/path/ |
| # Copy file from remote | scp user@host:/path/file.txt ./ |
📝 File Viewing & Editing
| # View file contents | cat file.txt |
| # View with pagination | less file.txt |
| # Edit with nano | nano file.txt |
| # Edit with vim | vim file.txt |
| # Show first 10 lines | head file.txt |
| # Show last 10 lines | tail file.txt |
| # Follow file updates | tail -f logfile.log |
🖥️ Process Management
| # List running jobs | jobs |
| # Kill process by PID | kill -9 1234 |
| # Kill process by name | pkill -f process_name |
| # Run in background | command & |
| # Bring job to foreground | fg %1 |
🔄 Permissions & Ownership
| # Change file permissions (read/write/execute for user/group/other) | chmod 755 file.sh |
| # Add execute permission | chmod +x script.sh |
| # Change file owner | chown user:group file.txt |