netstat — Network Connections and Statistics

netstat is a classic command for checking network connections, listening ports and routing information on Linux systems. On modern systems, ss is often preferred, but netstat is still useful on older servers and troubleshooting notes.

Show listening TCP and UDP ports

netstat -tuln

This lists listening TCP and UDP sockets with numeric addresses and ports.

Show programs using ports

sudo netstat -tulpn

The -p option shows the process using each socket. This is useful when you need to know which service is listening on a port.

Show routing table

netstat -rn

This shows the kernel routing table with numeric addresses.

For newer systems, the equivalent modern commands are usually ss -tuln and ip route.