Linux listening network services $ netstat -ntlp $ netstat -nulp $ netstat -nxlp

I usually run three separate commands, all of a sudden do not want to see a lot of all of the services listed. netstat -nalp is fine. But I would never use numeric option (I a little shallow view: IP address looks more convenient). 
Find all services that are running, check whether they should run. Check each listening port. PID and process ps aux list in the list of services that appears in netstat is the same. 

If there are several Java or what Erlang processes running on the server at the same time, each process can be found by PID are very important. 

Usually we recommend running a little low on each server service, if necessary, can increase the server. If you see thirty or forty listening ports open on a server, and that was to be a record, clean up free time back, reorganize server.