/Library/Ruby/Gems/1.8/gems/eventmachine-0.12.10/lib/eventmachine.rb:572:in `start_tcp_server': no acceptor (RuntimeError)
Seeing this error when trying to run your Rack or Sinatra webapp?
It’s probably because you’re already running something on the port you’re trying to use. This happens quite a bit if you’re using daemonized Rack apps that go off on their own after you close the controlling shell.
Use this command to see what’s happening on a port:
$ lsof -i :4567 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME ruby 74716 mathiasx 5u IPv4 0x073562a4 0t0 TCP *:tram (LISTEN)
It’ll help you see the PID of the process that’s hogging that port. Just be careful not to kill anything that should be on that port!