How to find process using TCP port?

Question

After starting a http a couple of times I get this error like an instance of Go has not stopped!?

listen tcp :9000: bind: address already in use

I have experienced something like this with nodejs too but I was able to kill the process.. Unfortunately it seems like I can't find the process id and kill it..

How to "free" the tcp port?

Answer 1

If you are on unix like system you can use netstat to find out which process is listening on a port:

sudo netstat -nlp | grep 9000

Turns out the -p option is not available on OS X. If you are using OS X you can do this:

lsof -n -i4TCP:$PORT | grep LISTEN

Who is listening on a given TCP port on Mac OS X?