Some days back I was facing an interesting problem. We have multiple tomcat instances configured on a single Linux box. The box was configured to have more than one internal ips. I needed to know which ports were active. Did some browsing on the net (essentially did a google search ;-)) and found a Linux command nmap.
Used the following command
nmap -sT -p
nmap -sT 127.0.0.1 -p 1-9000
This is the command to check ports from 1 to 9000 on the server 127.0.0.1. There is a -sS option available for users with root privileges but myself a lowly developer does not enjoy such rights.