Node.js errorNode.js: “listen EADDRINUSE: address already in use”

Why the port is taken, and the fix

1. 01

   An old copy of your server is still running

   “An attempt to bind a server (net, http, or https) to a local address failed due to another server on the local system already occupying that address.” Node.js, Errors: Common system errors

   A crashed terminal, a closed editor tab or a background job can leave the previous server running. Find the process that owns the port and stop it. Check what it is before you kill it, so you don’t stop a database or another app. Add /F to taskkill (or use kill -9) only if it refuses to stop. If docker ps shows a container publishing the port, stop the container instead.

   # macOS / Linux (listening process only)
   lsof -nP -iTCP:3000 -sTCP:LISTEN
   kill <PID>
   
   # Windows
   netstat -ano | findstr LISTENING | findstr ":3000 "
   taskkill /PID <PID>

2. 02

   Another app uses the same default port

   Ports 3000, 5000 and 8080 are defaults for many tools. On macOS 12 (Monterey) and later, the AirPlay Receiver listens on ports 5000 and 7000; turn it off in System Settings, General, AirDrop & Handoff, or use another port. Read the port from an environment variable so you can move it without editing code.

   const port = Number(process.env.PORT) || 3000;
   app.listen(port, () => console.log(`Listening on ${port}`));

3. 03

   Two servers start in the same process

   “This happens when another server is already listening on the requested port / path / handle.” Node.js, Net: server.listen()

   Calling listen twice, for example once in app.js and again in a test or a server.js that imports it, makes the second call fail. Export the app without listening, and call listen only in the entry file. In tests, use a test client that does not bind a port, or close the server after each run.

4. 04

   Restarts do not wait for the old process

   With nodemon or a process manager, the new copy can start before the old one has released the port. Close the server on SIGINT and SIGTERM, and tell nodemon to use SIGTERM, because its default restart signal is SIGUSR2: nodemon --signal SIGTERM server.js. Avoid running two watchers on the same project.

   const server = app.listen(port);
   for (const sig of ['SIGINT', 'SIGTERM']) {
     process.on(sig, () => server.close(() => process.exit(0)));
   }

Checked against the vendor’s docs on November 7, 2026: Node.js: Errors: Common system errors (EADDRINUSE); Node.js: Net: server.listen().

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