How to Kill a Process on a Port on Mac (localhost:3000, 5432, 8080)

The Problem: Something Is Already on That Port

You run npm run dev and get:

Error: listen EADDRINUSE: address already in use :::3000

This happens when a previous dev server didn't exit cleanly. The process is still running, holding the socket open.

The Basic Fix: lsof + kill

# Find what's on port 3000
lsof -i :3000

# Kill it (replace PID with the number from lsof output)
kill -9 PID

This works, but it has a critical flaw: it kills just that process. If your dev server is zsh → npm run dev → next-server, killing only next-server leaves the parent npm process running. It may respawn the server or remain as a zombie consuming memory.

The Correct Fix: Process Group Termination

# Get the PID of the port listener
PID=$(lsof -ti :3000)

# Get the PGID (process group ID)
PGID=$(ps -o pgid= -p $PID | tr -d ' ')

# Kill the entire process group gracefully
kill -TERM -$PGID

# If still alive after 3 seconds:
sleep 3 && kill -KILL -$PGID 2>/dev/null

This terminates the entire parent → child process hierarchy, ensuring no zombie workers remain.

Common Dev Port Reference

Port	Common Service
3000	Next.js, React dev server, Rails
4000	Gatsby, Nuxt.js
5432	PostgreSQL
6379	Redis
8080	Java apps, various APIs
8888	Jupyter Notebook
9000	PHP-FPM, SonarQube
27017	MongoDB

Using MacPilot's Port Manager

MacPilot's Port & Socket Manager shows you every listening socket alongside its full process ancestry tree (zsh → npm → next-server) and working directory. One click sends a graceful SIGTERM to the entire process group. If the process is stubborn, escalate to SIGKILL with a second click.

It also flags sockets bound to 0.0.0.0 (publicly exposed) vs 127.0.0.1 (localhost-only) — a quick security audit with no extra tools.