Linux / Server

Address already in use (EADDRINUSE)

The port you tried to bind is already taken by another process.

What it looks like

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

What does "Address already in use (EADDRINUSE)" mean?

Raised when a server tries to listen on a port another process already holds. Most often that other process is an earlier copy of the same server that never shut down, such as a dev server left running in another terminal.

What causes "Address already in use (EADDRINUSE)"?

A previous run of your server is still alive.
Another app uses the same port.
The port is in TIME_WAIT after a crash.

How do I confirm the cause?

Find what holds the port: lsof -i :3000 or ss -ltnp on Linux and macOS, netstat -ano | findstr :3000 on Windows.
Check whether it is an old copy of your own app, another app, or a container publishing the same port.
If nothing is listening but the error persists, the port may be in TIME_WAIT after a crash — it clears within a minute or two.

How do I fix "Address already in use (EADDRINUSE)"?

Find and kill the process (lsof -i :PORT / kill).
Use a different port.
Enable SO_REUSEADDR / wait for TIME_WAIT to clear.

How do I stop it happening again?

Shut the server down cleanly (handle SIGINT and SIGTERM and close the listener).
Make the port configurable (a PORT environment variable) so two services never have to fight over it.

Got a different error? Paste it into the Explain This Error tool → Identifies the family and the fix — runs locally, nothing uploaded.