Linux System Administration

Essential Commands

File Management

ls -la              # List files with details
cp source dest      # Copy files
mv source dest      # Move files
rm file            # Remove file
mkdir dirname      # Create directory
find . -name "*.log"  # Find files

User Management

useradd username   # Create user
passwd username    # Set password
usermod -aG sudo username  # Add to group
userdel username   # Delete user

Permissions

chmod 755 file     # Set permissions (rwxr-xr-x)
chown user:group file  # Change owner
chmod +x script.sh # Make executable

System Information

uname -a          # System info
df -h             # Disk usage
ps aux            # Running processes
top               # Process monitor

Package Management

apt update && apt upgrade    # Debian/Ubuntu
yum update && yum upgrade    # RedHat/CentOS
apt install package          # Install package

Networking

ifconfig          # Network interfaces
netstat -tuln     # Listening ports
ss -tuln          # Modern netstat
ping host         # Test connectivity
ssh user@host     # Remote login
scp file user@host:/path  # Copy over SSH

Best Practices

✅ Use sudo instead of root ✅ Regular backups ✅ Monitor logs ✅ Keep system updated ✅ Configure firewall ✅ Manage SSH keys ✅ Document changes