how to find out what port is listening

netstat command to find open ports

# netstat --listen
To display open ports and established TCP connections, enter:
$ netstat -vatn
To display only open UDP ports try the following command:
$ netstat -vaun
If you want to see FQDN (full dns hostname), try removing the -n flag:
$ netstat -vat

lsof Command Examples

To display the list of open ports, enter:
# lsof -i
To display all open files, use:
# lsof
To display all open IPv4 network files in use by the process whose PID is 9255, use:
# lsof -i 4 -a -p 9255