Essential Linux Commands Every Server Admin Needs

File & Directory Management

Command	Description
ls -la	List all files including hidden, with permissions
cd /path	Change directory
pwd	Show current directory path
mkdir -p dir/sub	Create directory and parents
cp -r src dest	Copy files/directories recursively
mv src dest	Move or rename files
rm -rf /path	Delete files/folders (no confirmation!)
find / -name "*.log"	Search for files by name
cat file.txt	Display file contents
tail -f /var/log/syslog	Stream live log output
grep -r "error" /var/log	Search file contents recursively

System Monitoring

Command	Description
top / htop	Live process monitor (install htop: apt install htop)
df -h	Disk usage by filesystem
du -sh /var/*	Folder sizes
free -h	RAM and swap usage
uptime	System uptime and CPU load average
ps aux --sort=-%cpu	All processes sorted by CPU usage
kill -9 PID	Force-kill a process
journalctl -f	Live system log stream
journalctl -u nginx	Logs for a specific service

Networking

ip addr                           # Show all IP addresses
ip route                          # Show routing table
ping 8.8.8.8                      # Test connectivity
curl -I https://Power Down.in      # Check HTTP headers
ss -tlnp                          # Show listening ports and processes
netstat -tlnp                     # Same (older systems)
traceroute 8.8.8.8                # Trace network path
dig Power Down.in                  # DNS lookup
nslookup Power Down.in             # Alternative DNS lookup
wget https://example.com/file.zip # Download a file

Package Management (Ubuntu/Debian)

apt update                    # Refresh package index
apt upgrade -y                # Upgrade all packages
apt install nginx -y          # Install a package
apt remove nginx              # Remove a package (keep config)
apt purge nginx               # Remove package AND config
apt autoremove -y             # Remove unused dependencies
apt search nginx              # Search for packages
dpkg -l | grep nginx          # Check if installed

File Permissions

chmod 755 /var/www             # rwxr-xr-x
chmod 644 /var/www/index.html  # rw-r--r--
chmod 600 ~/.ssh/id_ed25519    # rw------- (private key)
chown -R www-data:www-data /var/www/html  # Change ownership