Dhiru · dev watch

What's running on port 4321 on Mac, and how to stop it

Usually: Astro's dev server runs here.

See what's on port 4321

Open Terminal and run:

lsof -nP -iTCP:4321 -sTCP:LISTEN

The first column is the app, the second its PID (process ID).

Stop it

kill <PID>

If it's still listed a few seconds later, use kill -9 <PID>. Or stop whatever is on 4321 in one go:

kill $(lsof -t -iTCP:4321 -sTCP:LISTEN)

Other ports: 3000, 3001, 3306, 4000, 4200, 5000, 5173, 5432, 5555, 6006, 6379, 7000, 8000, 8080, 8081, 8787, 8888, 9000, 9229, 27017. All at once: see everything that's listening.