title: What is the meaning of "sandbox" in "docker run" command?
body: <p>I am running the <a href="https://registry.hub.docker.com/u/sequenceiq/spark/" rel="nofollow">Docker image with Apache Spark</a>:  </p>
  
  <pre><code>docker run -i -t -h sandbox sequenceiq/spark:1.2.1-ubuntu /etc/bootstrap.sh -bash
  </code></pre>
  
  <p>I can know the meaning of "<code>-i</code>", "<code>-t</code>" and "<code>-h</code>" after executing "<code>docker run --help</code>" command. But how can I explain the "<code>sandbox</code>" here? Is it a option of "<code>docker run</code>" command? I can't find it in the output of "<code>docker run --help</code>".</p>