title: Mongo stopped working after upgrading
body: <p>I recently upgraded mongodb from 2.6 to 3.4.1 and now it won't connect. The log shows:</p>
  
  <pre><code>root@synctup-stage:~# tail -30 /var/log/mongodb/mongodb.log
  2018-05-16T12:16:49.372+0000 [initandlisten] connection accepted from 127.0.0.1:40540 #17 (3 connections now open)
  2018-05-16T12:17:22.670+0000 [clientcursormon] mem (MB) res:43 virt:548
  2018-05-16T12:17:22.670+0000 [clientcursormon]  mapped (incl journal view):320
  2018-05-16T12:17:22.670+0000 [clientcursormon]  connections:3
  2018-05-16T12:21:34.334+0000 [conn17] end connection 127.0.0.1:40540 (2 connections now open)
  2018-05-16T12:21:44.046+0000 [initandlisten] connection accepted from 127.0.0.1:40542 #18 (3 connections now open)
  2018-05-16T12:21:44.054+0000 [conn18] end connection 127.0.0.1:40542 (2 connections now open)
  2018-05-16T12:22:22.682+0000 [clientcursormon] mem (MB) res:44 virt:548
  2018-05-16T12:22:22.682+0000 [clientcursormon]  mapped (incl journal view):320
  2018-05-16T12:22:22.682+0000 [clientcursormon]  connections:2
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] got signal 15 (Terminated), will terminate after current cmd ends
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] now exiting
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] dbexit: 
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: going to close listening sockets...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] closing listening socket: 8
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] closing listening socket: 9
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] removing socket file: /tmp/mongodb-27017.sock
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: going to flush diaglog...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: going to close sockets...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: waiting for fs preallocator...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: lock for final commit...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: final commit...
  2018-05-16T12:27:02.682+0000 [signalProcessingThread] shutdown: closing all files...
  2018-05-16T12:27:02.682+0000 [conn11] end connection 127.0.0.1:35824 (1 connection now open)
  2018-05-16T12:27:02.682+0000 [conn10] end connection 127.0.0.1:35822 (1 connection now open)
  2018-05-16T12:27:02.684+0000 [signalProcessingThread] closeAllFiles() finished
  2018-05-16T12:27:02.684+0000 [signalProcessingThread] journalCleanup...
  2018-05-16T12:27:02.684+0000 [signalProcessingThread] removeJournalFiles
  2018-05-16T12:27:02.686+0000 [signalProcessingThread] shutdown: removing fs lock...
  2018-05-16T12:27:02.686+0000 [signalProcessingThread] dbexit: really exiting now
  </code></pre>
  
  <p>Any gurus out there see what might be going on?</p>
  
  <p>It was working fine up until the upgrade and the upgrade seemed to go well.</p>
  
  <p>I get the following errors when trying to start the mongo shell:</p>
  
  <pre><code>MongoDB shell version v3.4.15
  connecting to: mongodb://127.0.0.1:27017
  2018-05-16T12:28:08.006+0000 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
  2018-05-16T12:28:08.006+0000 E QUERY    [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
  connect@src/mongo/shell/mongo.js:240:13
  @(connect):1:6
  exception: connect failed
  </code></pre>