Docker for Rails Developers

Rails tmp/pids/server.pid Not Cleaned Up

For some reason, occasionally upon terminating the app with Compose (pressing Ctrl-C), the Rails server doesn’t seem to shut down cleanly, and its server.pid file—which Rails stores in tmp/pids/—isn’t deleted. This means that upon starting the app again with:

$ docker-compose up

you may find yourself confronted by the following error in the output:

...
A server is already running. Check /usr/src/app/tmp/pids/server.pid
...

The existence of the pid file makes the Rails server starting up believe that there’s a server already running, so it won’t launch.

Rails saves the server.pid file in tmp/pids. Since we’re mounting our local app directory into the container, the file ends up in the ...