netstat
$ netstat [--all] [--list] [--tcp] [--udp] [--numeric] [--program] [--wide] [--extend]Display network connections
-a, --all: Display both listening and non-listening sockets-l, --list: Display only listening sockets-t, --tcp: Display only TCP network connections-u, --udp: Display only UDP network connections-n, --numeric: Display numerical addresses-p, --program: Show the PID and name of the program to which each socket belongs-W, --wide: Do not truncate IP addresses by printing out the whole symbolic host-e, --extend: Display more information