title: mongo createIndex background blocks the shell
body: <p>I am creating an index on a few Gigabits of documents.</p>
  
  <p>In my mongo shell, I ran this command:</p>
  
  <pre><code>db.positions.createIndex( { "imei": 1, "server_date": -1 }, { "background": true, "name": "positions_imei_server_date" } );
  </code></pre>
  
  <p>However I did not get the shell prompt back even with background set at true.</p>
  
  <p>If I look in the log, I see: </p>
  
  <pre><code>[conn13]   Index Build (background): 14129300/19197181 73%
  </code></pre>
  
  <p>So it seems that it is really running as a background task. However why did I not get back the prompt in the shell? Is it normal? If I type <kbd>CTRL</kbd>+<kbd>C</kbd> will it cancel my index?</p>
  
  <p>I am running the mongo 3.4.0</p>