title: Fail to Authenticate in mongo as localhost
body: <p>I use the latest mongo, and try to set the SuperUserAdmin as described in the Mongo Doc.</p>
  
  <pre><code>1) Start ./mongod --dbpath ../data    without auth
  2) Run ./mongo
  3) [mongo shell]: use admin
  4) [mongo shell]: db.addUser( { user: "admin",
                pwd: "abcde1234",
                roles: [ "userAdminAnyDatabase" ] } )
  5) [mongo shell]: db.shutdownServer()
  
  then i restart mongod with auth:
  6) ./mongod --auth --dbpath ../data
  7) Run mongo (as localhost) again: ./mongo -u admin -p abcde1234
  
  Then i get this error:
  Javascript executiion failed: Error: 18 {code:18, ok:0.0, errmsg: 'auth fails'} at src/mongo/shell/db.js:L228
  </code></pre>
  
  <p>I tried different username &amp;password, same thing.. </p>
  
  <p>what am i missing? I'm running on my Mac.</p>
  
  <p>anyone has any idea?</p>