title: Problems upgrading MongoDB
body: <p>I have difficulty updating mongodb from version 2.0.6 to the current 2.4. Please help</p>
  
  <p>Below is the log file that i get:</p>
  
  <pre><code>Tue May 14 08:02:03.339 [initandlisten] MongoDB starting : pid=1906 port=27017 dbpath=/mnt2/var/lib/mongodb/ 64-bit host=ip-10-131-65-73
  Tue May 14 08:02:03.339 [initandlisten] db version v2.4.3
  Tue May 14 08:02:03.339 [initandlisten] git version: fe1743177a5ea03e91e0052fb5e2cb2945f6d95f
  Tue May 14 08:02:03.340 [initandlisten] build info: Linux ip-10-2-29-40 2.6.21.7-2.ec2.v1.2.fc8xen #1 SMP Fri Nov 20 17:48:28 EST 2009 x86_64 BOOST_LIB_VERSION=1_49
  Tue May 14 08:02:03.340 [initandlisten] allocator: tcmalloc
  Tue May 14 08:02:03.340 [initandlisten] options: { dbpath: "/mnt2/var/lib/mongodb/" }
  Tue May 14 08:02:03.347 [initandlisten] journal dir=/mnt2/var/lib/mongodb/journal
  Tue May 14 08:02:03.347 [initandlisten] recover : no journal files present, no recovery needed
  Tue May 14 08:02:03.554 [initandlisten] build index backendtemp.system.users { user: 1, userSource: 1 }
  Tue May 14 08:02:03.557 [initandlisten] Duplicate key exception while trying to build unique index on backendtemp.system.users.  You most likely have user documents with duplicate "user" fields.  To resolve this, start up with a version of MongoDB prior to 2.4, drop the duplicate user documents, then start up again with the current version.
  Tue May 14 08:02:03.557 [initandlisten] exception in initAndListen: 11000 E11000 duplicate key error index: backendtemp.system.users.$user_1_userSource_1  dup key: { : "ad", : null }, terminating
  Tue May 14 08:02:03.557 dbexit: 
  Tue May 14 08:02:03.557 [initandlisten] shutdown: going to close listening sockets...
  Tue May 14 08:02:03.557 [initandlisten] shutdown: going to flush diaglog...
  Tue May 14 08:02:03.557 [initandlisten] shutdown: going to close sockets...
  Tue May 14 08:02:03.558 [initandlisten] shutdown: waiting for fs preallocator...
  Tue May 14 08:02:03.558 [initandlisten] shutdown: lock for final commit...
  Tue May 14 08:02:03.558 [initandlisten] shutdown: final commit...
  Tue May 14 08:02:03.572 [initandlisten] shutdown: closing all files...
  Tue May 14 08:02:03.573 [initandlisten] closeAllFiles() finished
  Tue May 14 08:02:03.573 [initandlisten] journalCleanup...
  Tue May 14 08:02:03.573 [initandlisten] removeJournalFiles
  Tue May 14 08:02:03.575 [initandlisten] shutdown: removing fs lock...
  Tue May 14 08:02:03.575 dbexit: really exiting now
  </code></pre>