"Port 8080 required by Tomcat v6.0 Server at localhost is already in use. The server may already be running in another process, or a system process may be using the port. To start this server you will need to stop the other process or change the port number(s)."

I have been seeing this error from Tomcat every time I reboot my Windows development box. It is easy enough to track down the process holding onto the port:

netstat -a -o

Now I know that the process PLEX760… is listening to port 8080. It is trivial to kill the process using Task Manager now that I know the process ID (3832), but I really want to know what this thing is, and why it is getting started. This brings me to my favorite Windows utility program, Process Explorer.

Using Process Explorer I can see where the actual exe lives on the local disk:

Under the services tab I can see that this is associated with a Windows service:

Going to:

Control Panel -> Administrative Tools -> Services

Lets me stop the service, and set it to manual start-up.

This little example does not even begin to scratch the surface in what information Process Explorer can provide about currently running applications. I highly encourage you to try it out next time you are trying to nail down what is going on with  a windows application.