title: Error when starting Docker daemon with user other than root (permission denied)
body: <p>I want to start the Docker daemon with a user other than root.</p>
  
  <p>I'm trying to start it with <code>docker daemon --host=unix:///var/run/docker.sock --host=tcp://0.0.0.0:2375 --storage-driver=vfs</code>.</p>
  
  <p>Sadly this error occurs:</p>
  
  <blockquote>
    <p>FATA[0000] Error starting daemon: open /var/run/docker.pid: permission
    denied</p>
  </blockquote>
  
  <p>When I look into the directory <code>/var/run/</code> I can't see any file named 
  <code>docker.pid</code>.</p>
  
  <p>Starting the service as <code>root</code> works without problems.</p>