Port 3000 Already in Use on Mac: How to Find and Free It

You start your dev server and immediately see:

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

Nothing else changed. You didn’t start another server. Yet something is holding port 3000 hostage.

Why This Happens

Port conflicts usually come from a process that crashed or was force-quit without releasing its socket. When a process exits uncleanly, the macOS kernel keeps the port bound until the process is fully gone or explicitly killed. The socket stays open even though nothing is actively listening on it.

This hits most often with Node.js servers, Rails applications, and other dev frameworks that default to port 3000. You close your terminal window, the process gets stuck in limbo, and the next time you try to start a fresh server it collides with the leftover binding.

Finding the Process

The lsof command (list open files) shows which process owns a port. Run this in Terminal:

lsof -i :3000

You’ll get output like this:

COMMAND   PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node     8412  aaron   23u  IPv6 0x1234abcd5678      0t0  TCP *:3000 (LISTEN)

Here’s what each column means:

COMMAND: the executable name holding the port
PID: the process ID you’ll use to kill it
USER: the account running the process
FD: the file descriptor (the u suffix means read/write)
TYPE: IPv4 or IPv6
NODE: the protocol (TCP here)
NAME: the port and its state (LISTEN means it’s actively bound)

The PID column is what you need for the next step.

Killing It

Once you have the PID, send it SIGKILL:

kill -9 8412

The -9 flag sends SIGKILL, which forces the process to exit immediately. Unlike SIGTERM (signal 15), SIGKILL cannot be caught or ignored by the process. It terminates without any cleanup, which is exactly what you want when a process is already stuck.

If you want to do it in one line without looking up the PID:

kill -9 $(lsof -ti :3000)

The -t flag tells lsof to output only the PID, with no column headers. That makes it safe to pipe directly into kill.

When lsof Shows Nothing

If lsof -i :3000 returns no output but you’re still getting EADDRINUSE, the port is probably in TIME_WAIT state. This is an OS-level cooldown period that happens after a socket closes normally. The kernel holds onto the port for a short window (typically around 30 seconds on macOS) to handle any late-arriving packets from previous connections.

There is nothing to kill in this case because there is no process. Wait a minute and try again, or point your server at a different port temporarily while the cooldown clears.

Other Dev Ports

The same lsof and kill commands work for any port. Common ones developers run into:

5000: Python Flask, older Rails
8080: Java servlet containers, many proxies
8000: Django, Python HTTP servers
5173: Vite
4200: Angular CLI

Just swap the port number in lsof -i :PORT and kill -9 $(lsof -ti :PORT).

Using Portie

If you’d rather not memorize flags, Portie shows every open port on your Mac with its owning process, refreshed automatically every 3 seconds. The live list is free. You can see at a glance what’s bound to port 3000 and which app owns it.

The $8.99 one-time unlock adds the ability to kill a process directly from the list, with either SIGTERM or SIGKILL, without opening Terminal. If you spend any time in local development, the two-second kill-from-list workflow pays for itself quickly.