How can I check which TCP/IP ports are in use?

Question

I just installed Tomcat on top of existing installations of a bunch of web application servers and I eventually get an exception saying that the port is in use.

My question is how can I check which TCP / IP ports are currently in use?

Answer 1

On Windows use the following command:

netstat -aon | more

You can remove the more operand followed by a pipe if your command line window buffer is large enough to scroll through the list.

On UNIX and the Mac (OS X):

netstat -na | grep LISTEN

You can add grep 80 followed by a pipe sign, for example, to list all ports starting with 80 (including 8080, 8081, and so on...) being listened to.