Comment 13 for bug 1375836

EDIT: Do not do the above. The package is obsolete.
Use fuser -a /etc/services then use ps <PID>, replace <PID> with the process ID that comes up in fuser:
Example:
root@web2:~# fuser -a /etc/services
/etc/services: 4567
root@web2:~# ps 4567
  PID TTY STAT TIME COMMAND
4567 tty1 Ss 0:01 <command>