title: How to export all collections in MongoDB?
body: <p>I want to export all collections in MongoDB by the command:  </p>
  
  <pre><code>mongoexport -d dbname -o Mongo.json
  </code></pre>
  
  <p>The result is:<br>
  No collection specified!  </p>
  
  <p>The manual says, if you don't specify a collection, all collections will be exported.<br>
  However, why doesn't this work?</p>
  
  <p><a href="http://docs.mongodb.org/manual/reference/mongoexport/#cmdoption-mongoexport--collection" rel="noreferrer">http://docs.mongodb.org/manual/reference/mongoexport/#cmdoption-mongoexport--collection</a></p>
  
  <p>My MongoDB version is 2.0.6.</p>