Find specific ports in use

Jan 18, 2026

From time to time I always try to spin up a quick server only to discover that there is a process which is already using that specifc port that you’re trying to acquire. A lot of the times, at least for me, those processes are not attached to a TTY anymore so there’s no way to ctrl-c it and free the port. In that case, you’d need to find the process and kill it with fire.

On macOS there’s a very simple command that you can use to immediately tell the PID which is bound to that port.

$ lsof -i :8000
COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
Python  77918 matt    4u  IPv6 0xb38865aa8736f21b      0t0  TCP *:irdmi (LISTEN)

This tells you that process 77918 is using port 8000 and is listening for TCP connections on * all interfaces.

You can tell if a process has a tty attached by running

$ ps -p 77918 -o pid,tty
PID TTY
77918 ttys002

This is still attached to a terminal session so you can technically open that session and ctrl-c it, but in case the process is not attached to a tty you can claim that port back with

$ kill -p 77918