It’s never too late to learn something that would have saved your hide eons ago:

netstat -lntp

Produces output that looks like:

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN      541328/node