title: Why does SparkContext randomly close, and how do you restart it from Zeppelin?
body: <p>I am working in Zeppelin writing spark-sql queries and sometimes I suddenly start getting this error (after not changing code):</p>
  
  <pre><code>Cannot call methods on a stopped SparkContext.
  </code></pre>
  
  <p>Then the output says further down:</p>
  
  <pre><code>The currently active SparkContext was created at:
  
  (No active SparkContext.)
  </code></pre>
  
  <p>This obviously doesn't make sense.  Is this a bug in Zeppelin?  Or am I doing something wrong?  How can I restart the SparkContext?</p>
  
  <p>Thank you</p>