Node.js Port Already in Use (Error: listen EADDRINUSE)

# macOS and Linux:
lsof -i :3000
# Alternative Linux socket statistics:
ss -lptn 'sport = :3000'

# Windows (PowerShell):
Get-Process -Id (Get-NetTCPConnection -LocalPort 3000).OwningProcess

# Windows (Command Prompt):
netstat -ano | findstr :3000

# macOS and Linux (graceful then force):
kill -15 <PID>
# Or force kill if hung:
kill -9 <PID>

# Fast one-liner to kill whatever is on port 3000 (Linux/macOS):
fuser -k 3000/tcp
# Or with npx utility:
npx kill-port 3000

# Windows (Command Prompt):
taskkill /F /PID <PID>

# Windows (PowerShell):
Stop-Process -Id <PID> -Force

# Find container bound to port 3000:
docker ps --filter 'publish=3000'

# Stop the container:
docker stop <container_id_or_name>

# Or quickly run your dev server on a non-conflicting port:
PORT=5001 npm run dev

import express from 'express';

const app = express();

// Read port from environment or fallback to 3000
const DEFAULT_PORT = parseInt(process.env.PORT || '3000', 10);

function startServer(port: number) {
  const server = app.listen(port, () => {
    console.log(`Server actively running on http://localhost:${port}`);
  });

  server.on('error', (err: NodeJS.ErrnoException) => {
    if (err.code === 'EADDRINUSE') {
      console.warn(`Port ${port} is in use, attempting fallback to port ${port + 1}...`);
      startServer(port + 1);
    } else {
      console.error('Server error:', err);
    }
  });
}

startServer(DEFAULT_PORT);

import http from 'http';
import app from './app';

const server = http.createServer(app);
const PORT = process.env.PORT || 3000;

server.listen(PORT, () => {
  console.log(`Application listening on port ${PORT}`);
});

// Clean socket shutdown handlers
function shutdown(signal: string) {
  console.log(`Received ${signal}. Closing HTTP server gracefully...`);
  server.close(() => {
    console.log('HTTP server closed. Exiting process.');
    process.exit(0);
  });

  // Force close after 10s if connections refuse to finish
  setTimeout(() => {
    console.error('Forcefully terminating process due to lingering connections.');
    process.exit(1);
  }, 10000);
}

process.on('SIGTERM', () => shutdown('SIGTERM'));
process.on('SIGINT', () => shutdown('SIGINT'));