EADDRINUSE

What is EADDRINUSE?

EADDRINUSE stands for 'Error: Address Already in Use'. It is thrown when Node.js attempts to bind a server or listener socket to a network port or IP address that is already active and occupied by another process on your operating system.

Common Causes

• Background App Hanging: An older instance of your server failed to close properly and is still holding the port in the background.
• Duplicate Dev Tool Servers: Another dev server (e.g. React/Vite/Docker) is already listening on the requested port.
• TIME_WAIT Port Locking: The operating system has temporarily locked the port during socket recycling (TIME_WAIT).

Common Mistakes

• Failing to close VS Code terminals or PM2 background instances before starting node processes again.
• Binding Docker container ports to host ports that are already occupied by host database services.

How to Fix

Framework-Specific Examples

const startServer = (port) => {
  const server = app.listen(port, () => {
    console.log(`Server successfully started on port ${port}`);
  });

  server.on('error', (err) => {
    if (err.code === 'EADDRINUSE') {
      console.log(`Port ${port} is occupied. Trying port ${port + 1}...`);
      startServer(port + 1);
    }
  });
};

Server Configuration Examples

Listen 8080

Best Practices

• Use variable PORT bindings derived from process.env.PORT configurations.
• Check active ports using automated build check scripts.

Frequently Asked Questions (FAQ)