Kill a process that listens on a port

You forgot to shut down a development server, and now it’s running in the background, taking up your favorite port. Terminate it mercilessly.

You’ve started a development server on your favorite :8080 localhost port and closed your IDE. But the server is still running in the background and if you try to start a new one, you get a message similar to this:

ERROR: listen tcp :8080: bind: address already in use

Yeah, me too. Let’s track it down and kill it for good.

List process listening on a port

lsof -i:8080

For me, this yields this result:

COMMAND   PID           USER   FD   TYPE            DEVICE SIZE/OFF NODE NAME
main    65536 vojtechstruhar    3u  IPv6 0xd9effee8308abdb      0t0  TCP *:http-alt (LISTEN)

See the PID column? That what we're after. Copy this process id number and terminate it:

kill 65536

If this doesn’t help, you can add the -9 flag, so that the process is forcibly terminated.

Shorthand

You can use the -t flag for the lsof command, so that only the PID of the process is printed. We can use this in a beautiful one-liner:

kill -9 $(lsof -t -i:8080)

If you find yourself doing this often, I’d say create a helper function in your .bashrc or similar:

function portkill {
	if [ "$#" -lt 1 ]; then
		echo "Supply a port to kill as a first argument."
		return 1
	fi
	
	echo "Killing process on port $1"
	kill -9 $(lsof -t -i:$1)
}

Now that this function is available to you in your shell by default, just call portkill 8080 and you are good to go :)

Originally published at https://www.vojtechstruhar.com.