title: Xvfb appears like already running, but no lock found
body: <p>I'm trying to launch Xvfb on a specific display, but I get this error message:<br><br></p>
  
  <pre><code>(EE) 
  Fatal server error:
  (EE) Server is already active for display 42
      If this server is no longer running, remove /tmp/.X42-lock
      and start again.
  (EE)
  </code></pre>
  
  <p>But when I look for <code>/tmp/.X42-lock</code>, it doesn't exist. How can I do to make the display 42 available again?<br><br>(I've tried with other displays, I works the first time, but then the display is not available anymore, which seems logic).
  <br><br>I've found a workaround but I think it's not very clean:</p>
  
  <pre><code>kill $(ps aux | grep 'Xvfb' | awk '{print $2}')
  // or...
  killall Xvfb
  </code></pre>
  
  <p>I would like to know if there's a cleaner way to stop Xvfb processes.</p>