Finding and Killing Processes By Port on Unix-like Systems

Another snippet post! Snippets are my attempt to write short posts about common problems or short concepts that I run into during development.

This happens from time to time to me, particularly with runaway Node processes. You try to start your app on localhost, but get a message like: EADDRINUSE, Address already in use or maybe listen tcp 127.0.0.1:3000: bind: address already in use. You don't have anything running on the port that you can find to stop, though, so what do you do?

lsof to the Rescue

lsof is a Unix command that means “list open files,” which means it lists files that are opened by processes running on your system. By default running lsof will display a huge amount of info, because at any given time there are a ton of processes running on your machine.

To narrow down the specific process that is running on a given port, use the -i flag. For example, to list the process running on port 3000, run: lsof -i :3000. Note the colon in there!

This will print some columnar data for you. It might look something like this:

COMMAND  PID  USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node    5750 hanna   28u  IPv4 0x66edcffc34e07861      0t0  TCP *:hbci (LISTEN)

The important info here is PID, which stands for Process Identifier.

kill the Process!

Now, you can use this PID to kill the runaway process with the kill command! I always pass the -9 flag to kill. This specifically passes a KILL signal to that process, which will effectively kill frozen or unresponsive processes.

To follow along with the example above, this is how I would kill that pesky Node process I found with lsof above:

kill -9 5750
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