title: MongoDB won't start after server crash
body: <p>My Ubuntu computer had crashed, and when I restarted it MongoDB wasn't working. I tried the following commands, and got the following output:</p>
  
  <pre><code>$ mongo
  Error: couldn't connect to server 127.0.0.1:27017 src/mongo/shell/mongo.js:91
  exception: connect failed
  
  $ service mongodb status
  mongodb stop/waiting
  
  $ service mongodb restart
  stop: Unknown instance: 
  start: Rejected send message, 1 matched rules; type="method_call",
         sender=":1.57" (uid=1000 pid=2227 comm="start mongodb ")
         interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)"
         requested_reply="0"
         destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")
  
  $ tail /var/log/mongodb/mongodb.log
  [initandlisten] exception in initAndListen: 12596 old lock file, terminating
  dbexit: 
  [initandlisten] shutdown: going to close listening sockets...
  [initandlisten] shutdown: going to flush diaglog...
  [initandlisten] shutdown: going to close sockets...
  [initandlisten] shutdown: waiting for fs preallocator...
  [initandlisten] shutdown: closing all files...
  [initandlisten] closeAllFiles() finished
  dbexit: really exiting now
  </code></pre>
  
  <p>(Output reformatted to match website layout.)</p>
  
  <p>What happened? How can I fix it?</p>