Why PM2 Is Not Launching Your Node.js App—and How to Fix It

Broken Your Node.js PM2 — and How to Fix It

Have you ever faced the frustration of manually running your Node.js app only for it to work perfectly—and yet, when launching it via PM2, it stubbornly refuses to respond? This is a surprisingly common issue, but fortunately, one that can often be resolved with a systematic approach.

In modern production environments, PM2 is a trusted manager for running Node.js processes reliably. But when things go wrong, it can feel like a black box—your app shows as “online” yet fails to respond. This blog will walk you through the most frequent culprits, structured troubleshooting steps, and production-level hardening tips to ensure your app stays up and running smoothly.

Common Reasons PM2 Fails to Launch Your Node Process

• Script Path or Filename Errors: A misconfigured script path may lead to silent failures. Verify file references like server/index.js.
• Application Not Listening on the Expected Port: Ensure your app is binding and listening on the correct port.
• Daemon Mode & Execution Context (Especially on Windows): GUI apps may not launch correctly without the --no-daemon flag.
• Missing System Startup Configuration: Without running pm2 startup and enabling systemd, apps won’t auto-start on reboot.
• Node Version Mismatch: After Node upgrades (e.g., via NVM), reinstall and update PM2 to maintain compatibility.
• Cluster Mode Port Conflicts: Avoid EADDRINUSE errors by assigning unique ports or using fork mode.

Step-by-Step Troubleshooting Guide

1. Verify Script Path & Logging
   Use pm2 logs and pm2 show <app> to inspect the app’s status and confirm the script path.
2. Confirm App is Listening on the Correct Port
   Use netstat, lsof, or curl to ensure the app binds to the expected port.
3. Use --no-daemon if Needed
   Launch with pm2 start app.js --no-daemon on systems that require GUI compatibility.
4. Configure System Startup Properly
   Run:

   pm2 startup
   # Follow systemd instructions
   pm2 save

5. Reinstall PM2 After Node Updates
   After switching Node versions, reinstall PM2 and run pm2 update.
6. Avoid Port Conflicts in Cluster Mode
   Assign unique ports or switch to fork mode to prevent errors.

Best Practices for Production Stability

• Use ecosystem.config.js to define mode, port, memory limits, and restart policies.
• Implement logging and health checks using --watch, --max-memory-restart, and structured formats.
• Integrate monitoring tools like ELK, Better Stack, or CloudWatch.
• Ensure proper handling of unhandled promise rejections to avoid silent crashes.

FAQs

• Why does PM2 say my app is “online,” but it’s not responsive?
  Likely due to incorrect port binding or silent failure in the startup routine.
• How do I make PM2 launch my app after reboot?
  Use pm2 startup followed by pm2 save to persist processes.
• Why won’t my GUI Node app start with PM2?
  Try --no-daemon or start via npm scripts.
• What should I do after upgrading Node?
  Reinstall PM2 and run pm2 update to sync versions.

Conclusion

When PM2 isn’t launching your Node.js app, the root cause is usually in environment or configuration. Use this guide to diagnose script path errors, port issues, version mismatches, and system startup configs. With proper setup, PM2 becomes an indispensable tool for Node.js app stability.