title: Can not unmount a device using "umount" in Docker
body: <p>I don't know why but, umount is not working in docker.</p>
  
  <pre><code>umount: loop3/: must be superuser to umount
  </code></pre>
  
  <p>Let me share one more thing that is 
  It creates <code>loop3</code> under <code>/mnt/loop3</code> in real machine. Which is most unexpected thing for me, because promises pure virtual environment. </p>
  
  <p>Why? Any solution?</p>
  
  <h3>Scenario :</h3>
  
  <p>I created docker <code>ubuntu:13.04</code> to create cross compilation environment. </p>
  
  <ul>
  <li><p>Docker Linux machine (ubuntu):</p>
  
  <pre><code>Linux 626089eadfeb 3.10.45-1-lts #1 SMP Fri Jun 27 06:44:23 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
  </code></pre></li>
  <li><p>Linux Machine (rch Linux):</p>
  
  <pre><code>Linux localhost 3.10.45-1-lts #1 SMP Fri Jun 27 06:44:23 UTC 2014 x86_64 GNU/Linux
  </code></pre></li>
  </ul>
  
  <h3>Docker Info</h3>
  
  <pre><code>Client version: 1.0.1
  Client API version: 1.12
  Go version (client): go1.3
  Git commit (client): 990021a
  Server version: 1.0.1
  Server API version: 1.12
  Go version (server): go1.3
  Git commit (server): 990021a
  </code></pre>