title: Error on Docker Pull - "Layer already being pulled by another client"
body: <p>I'm new to docker and have followed the installation instructions on their site <a href="https://docs.docker.com/installation/ubuntulinux/" rel="nofollow noreferrer">here</a>.</p>
  <p>The installation completed successfully:</p>
  <pre><code>docker -v
  Docker version 1.8.1, build d12ea79
  </code></pre>
  <p>but when I try to run</p>
  <pre><code>sudo docker run hello-world
  </code></pre>
  <p>I get the following:</p>
  <pre><code>Unable to find image 'hello-world:latest' locally
  latest: Pulling from library/hello-world
  
  535020c3e8ad: Pulling fs layer 
  af340544ed62: Layer already being pulled by another client. Waiting. 
  af340544ed62: Layer already being pulled by another client. Waiting.
  </code></pre>
  <p>This then continues to hang indefinitely.</p>
  <p>I have tried restarting the service and my entire machine. I always get the same problem.</p>
  <p>Any idea what's causing this or how to resolve?</p>