Netstat

Displays network-related information such as open connections, open socket ports, etc.

List all ports:

      netstat --all

  List all listening ports:

      netstat --listening

  List listening TCP ports:

      netstat --tcp

  Display PID and program names:

      netstat --program

  List information continuously:

      netstat --continuous

  List routes and do not resolve IP addresses to hostnames:

      netstat --route --numeric

  List listening TCP and UDP ports (+ user and process if you're root):

      netstat --listening --program --numeric --tcp --udp --extend