How to check which ports are listening on Ubuntu
If you are running your own vps, or even doing local development on an Ubuntu, sometimes your application wont start because it screams that another port is already listening on the port you are trying to setup your application on. To see which processes are listening on a port, simply issue the following command.
You will see a tabular list of processes and the ports they are currently listening on.
sudo netstat -tulpn