netstat

Displays various networks related information such as open connections, open socket ports etc.

• List all ports:

netstat -a

• List all listening ports:

netstat -l

• List listening TCP ports:

netstat -t

• Display PID and program names:

netstat -p

• List information continuously:

netstat -c

• List routes and do not resolve IP to hostname:

netstat -rn

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

netstat -lepunt