A server is already running. Check /tmp/pids/server.pid Ruby / Rails Origin: Application & API OSI layer 7 · Application Last updated 5 Nov 2026

Rails: A server is already running (pid: 12345, file: /app/tmp/pids/server.pid). Exiting

Rails thinks another server is running because a stale server.pid exists (often after a crash or in Docker).

Exact message you may see A server is already running. Check /tmp/pids/server.pid.A server is already running (pid: 12345, file: /app/tmp/pids/server.pid)A server is already running. Check /app/tmp/pids/server.pidExiting rails server already running pidPuma pid file exists
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Seen on: Ruby Docker Linux

Meaning

If no server runs, delete tmp/pids/server.pid and start again. In Docker add rm -f tmp/pids/server.pid to the entrypoint. If a server does run, find it (lsof -i :3000) and stop it, or use another port (-p 3001).

Common causes

  • Stale pid file after crash/forced stop
  • Container restart reusing a volume with the pid file
  • Another Rails server really running
  • Port 3000 in use
  • Mounted tmp shared between containers

⚡ Quick fix

  1. rm -f tmp/pids/server.pid
  2. Docker entrypoint: rm -f /app/tmp/pids/server.pid
  3. Check lsof -i :3000 for a real process

Detailed fix by platform

Linux

  1. lsof -i :3000; rm -f tmp/pids/server.pid; bin/rails s

How to diagnose

  1. Process — Really running?
  2. Pid file — Stale?
  3. Docker — Entrypoint cleans?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Application & API. Errors that are often confused with or caused by this one (click to open):

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