The following error can be encountered when running multiple servers:

> Error: Address already in use
> Error: listen EADDRINUSE

This is because the port has already been bound to a running server and now another server is trying to listen on that port.

There are 2 things that can be done:

1. Start your server on a different port.
2. Or free the port by killing the process associated with it.

Warning: If you choose the 2nd option, make sure you’re not killing anything important.

Getting the pid

Use lsof to get the process id (pid) associated with the port:

$ lsof -ti :<PORT> # replace <PORT> with the port number

Killing the pid

To kill the process associated with the port:

$ kill $(lsof -ti :<PORT>) # replace <PORT> with the port number

There may be a scenario where you’ll need to pass the SIGKILL signal to stop and kill the process immediately:

$ kill -9 $(lsof -ti :<PORT>)

Use sudo if you don’t have permissions:

$ sudo kill -9 $(lsof -ti :<PORT>)

And Unix users can accomplish the same thing with fuser:

$ fuser -k <PORT>/tcp # replace <PORT> with the port number