How do I find which process is using port 3000?

Run lsof -i :3000 on macOS or Linux. On Linux without lsof, use ss -ltnp | grep ':3000'.

How do I kill the process using a port?

Send SIGTERM first with kill -15 , and only force it with kill -9 if it is ignored. As a one-liner: kill -9 $(lsof -ti tcp:3000). On Linux, fuser -k 3000/tcp also works.

Why does a port stay busy after the server stops?

Either a child process still holds the socket, or the socket is in TIME_WAIT. A live LISTEN owner has a PID you can kill; TIME_WAIT clears by itself in a couple of minutes.

Which project is using port 3000?

lsof hands you a PID and a binary name. With six dev servers running that reads as node 41233, node 41871, node 42104 — and none of them tells you which project you are about to kill. portman does.

A menu-bar (macOS) or system-tray (Linux) app that lists only your dev servers — with the detected project name and framework — and lets you open, copy, reveal or kill each one in a click. OS daemons are filtered out, so you see what you actually started.

Six dev servers, six different projects — and one click to stop any of them.

Detects Node, Bun, Deno, Python, Go, Rust, Elixir, Ruby, PHP, Java, .NET, Ollama
Reads the project name from package.json, pyproject.toml, go.mod, Cargo.toml, composer.json
Names the framework: Next.js, Nuxt, Vite, Remix, Astro, SvelteKit, Angular, NestJS, FastAPI, Django, Flask, Rails, Laravel, Spring Boot, Phoenix, Axum
Per entry: uptime, PID, CPU, memory, and a health dot — does the port still accept connections?
One static Go binary, a few MB of RAM, ~0% CPU idle. Nothing leaves your machine.

Install

Linux and macOS — npm

npm install -g @forgebay/portman
portman

On Linux, if the tray icon does not appear: sudo apt-get install -y libgtk-3-0 libayatana-appindicator3-1

macOS — Homebrew

brew install forgebay/tap/portman
portman

Manual

Grab a binary from the releases page. On Linux, extract and run ./portman/install.sh; on GNOME, enable the AppIndicator and KStatusNotifierItem extension so the tray icon shows.

macOS: the app is not code-signed yet. The first launch is blocked by Gatekeeper — right-click the app and choose Open to get the "open anyway" prompt. A signed build needs a paid Apple Developer account; it is not in place yet, and saying so is more useful than letting you hit a dead end.

Source on GitHub

Just need the command?

# macOS and Linux — what is listening on port 3000
lsof -i :3000

# Linux, without lsof
ss -ltnp | grep ':3000'

Kill it

# ask it to shut down cleanly first (SIGTERM)
kill -15 <PID>

# still there? force it (SIGKILL)
kill -9 <PID>

# one-liner, macOS and Linux
kill -9 $(lsof -ti tcp:3000)

# Linux alternative
fuser -k 3000/tcp

Prefer -15 over -9. SIGTERM lets the process flush writes and close database connections. SIGKILL gives it no chance — reach for it only when the polite signal is ignored.

Honest alternatives

Several apps solve this, most of them free. If one fits you better, use it — the list is here so you do not have to go find it.

App	Platform	Notes
Ports (BigLittleApps)	macOS 14+	Free, native SwiftUI. Closest match feature-for-feature.
PortWatcher	macOS	Free. SIGTERM then SIGKILL fallback.
PortKiller	macOS	Free.
devglow	macOS	Free. Also runs your commands, ships an MCP server for AI coding tools.
Port Collision Radar	macOS	Free. Watches for a port being taken over.
portman	macOS + Linux	Free, MIT. The only one here that runs on Linux; single Go binary.

So: on macOS you have good free choices. On Linux, portman is the option.

FAQ

Why does the port stay busy after I stop the server?

Usually the parent process died but a child kept the socket, or the socket sits in TIME_WAIT. lsof -i :3000 shows the difference: a live LISTEN owner has a PID you can kill, whereas TIME_WAIT clears on its own within a couple of minutes.

Can I kill a port owned by another user?

Not without elevation. Ports owned by other users or by the system report no PID unless you are root, so portman hides them — it manages your own processes.

Does it phone home?

No network calls, no telemetry, no accounts. It reads local process state and that is all.

Windows?

Not supported. For now: netstat -ano | findstr :3000 then taskkill /PID <pid> /F.