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

-Display PID and program names

netstat -p

-Find out which port a process is running (e.g. find out which port ssh is listening on)

netstat -ap | grep ssh

-Find out which process is listening on a particular port

netstat -ap | grep ':80'