title: Unicorn says "Error opening file for reading: Permission denied"
body: <p>I'm running a rails 3 application running on unicorn, every now and then I get this message:</p>
  
  <blockquote>
    <p>Error opening file for reading: Permission denied</p>
  </blockquote>
  
  <p>and that's it. I don't know what file or what component is trying to opening it. It doesn't happen on each request or any other external event that I can figure out.</p>
  
  <p>Any ideas what might be going on or how to try to figure it out?</p>
  
  <p>I tried searching for "Error opening file for reading" on all the gems I'm using, with no luck.</p>