title: How to configure writeConcernMajorityJournalDefault: true?
body: <p>I am new to Mongodb and I would like to configure the writeConcernMajorityJournalDefault in mongodb.</p>
  
  <p>I tried to added to the mongo.conf and restart the service but failed.
  I tried to use the command in Mongodb shell and run:</p>
  
  <pre><code>cfg = rs.conf()
  cfg.writeConcernMajorityJournalDefault = true
  rs.reconfig(cfg)
  </code></pre>
  
  <p>It still fail, do miss something of it?
  Thanks</p>