title: X11: run a gnome app as another user
body: <p>I have ubuntu + x11 + gnome.</p>
  
  <p>I want to run a graphical application as another user.</p>
  
  <p>However, when I start it from the command line using <code>sudo -u otheruser app</code> I get the error "No protocol specified".</p>
  
  <p>How can I work arround this?</p>