I'm using vagrant as my virtual machine for a project and kept running into my port not shutting down completely after exiting the rails server.
vagrant@precise32:/vagrant$ rails s=> Booting Thin=> Rails 3.2.16 application starting in development on http://0.0.0.0:3000=> Call with -d to detach=> Ctrl-C to shutdown serverA server is already running. Check /vagrant/tmp/pids/server.pid
Solution was to check the port and to kill the process with the pid:
$ lsof -wni tcp:3000
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAMEruby 12365 vagrant 9u IPv4 114859 0t0 TCP *:3000 (LISTEN)
kill -9 12365