A One-Liner For Freeing Ports on OS X

bash

⛓ TL;DR

One of my most-frequently searched dev tasks over the course of my career thus far has been the “how do I find what process is on a port” to “how do I kill a given process” wombo-combo — there’s always some memory-leaky service running that ctrl+c isn’t tough enough for. Figured it’d be good to write a quick shell function for doing just this. Before I get into the explainer, here’s the code:

function killport {
	echo '🚨 Killing all processes at port' $1
	lsof -ti tcp:$1 | xargs kill
}

This bad boy can also be found as a script in Gist form on GitHub.

Sorry, this guide doesn’t currently solve for Windows or Linux systems, as far as I know. If y’all have an analogous solution, I’d happily include it in this post :)

⛓ Finding the offending process

After defining our function and adding some cute helper text, we can use lsof (list open files) to find processes that match our criteria. The manual for the lsof says:

An open file may be…a stream or a network file (Internet socket, NFS file or UNIX domain socket.)

Sounds like exactly what we’re on the hunt for. We’ll pass a couple of options to make this work as a function:

-t: The lower-case version of the -T flag sets some preferences for the output we get from running lsof. Specifically, -t returns only the PID, which is useful for piping this output to the kill command.
-i: This flag tells lsof to specifically look for matching internet addresses. We can pass the port we’re looking for in the format [protocol]:[port].

The protocol will be TCP, and then we can use a bash positional parameter to accept the port number as an argument to our killport function:

lsof -ti tcp:$i

⛓ Killing in the port of

Now that we have the PID of the process that is running on the port we want closed, we can send that over to the kill command. We’ll use a bash pipe and the xargs command to pass that information on.

All the pipe is doing here is passing the output of lsof to xargs, and all xargs is doing is taking some input and providing it as an argument to the kill command. All-told, that comes out to:

lsof -ti tcp:$i | xargs kill

That’s digital plumbing babey; we’re doing steampunk in cyberspace — and they said it couldn’t be done.

⛓ Conclusion

Gosh, thanks for reading, and gosh I hope it was useful! I am very certain there are one thousand and one enhancements that could be made for this puppy, so if you’d like to hit me with the Um Actually To End All Um Actuallies, shoot me an email. Like I mentioned earlier, I’d also love to make this article serve Windows and Linux users, so def get in touch about that too :D

A One-Liner For Freeing Ports on OS X

⛓ TL;DR

⛓ Finding the offending process

⛓ Killing in the port of

⛓ Conclusion

Further Reading