title: docker container won't start because an existing pid file
body: <p>When I start a docker container it fails because an existing pid file:</p>
  
  <pre><code>[root@newhope sergio]# docker logs sharp_shockley 
  httpd (pid 1) already running
  httpd (pid 1) already running
  httpd (pid 1) already running
  httpd (pid 1) already running
  </code></pre>
  
  <p>How can I remove such a file, because I don't find it.</p>
  
  <pre><code>[root@newhope sergio]# docker version
  Client version: 1.4.1
  Client API version: 1.16
  Go version (client): go1.3.3
  Git commit (client): 5bc2ff8/1.4.1
  OS/Arch (client): linux/amd64
  Server version: 1.4.1
  Server API version: 1.16
  Go version (server): go1.3.3
  Git commit (server): 5bc2ff8/1.4.1
  
  [root@newhope sergio]# find / -name "httpd.pid"
  find: ‘/run/user/1000/gvfs’: Permiso denegado
  </code></pre>