If you try to run mongod but it fails to start and have this error in the log file (/var/log/mongodb/mongodb.log) you’ll have to repair your db.
************** Unclean shutdown detected. Please visit http://dochub.mongodb.org/core/repair for recovery instructions. ************* Thu Dec 5 14:42:47.209 [initandlisten] exception in initAndListen: 12596 old lock file, terminating Thu Dec 5 14:42:47.209 dbexit: Thu Dec 5 14:42:47.209 [initandlisten] shutdown: going to close listening sockets... Thu Dec 5 14:42:47.209 [initandlisten] shutdown: going to flush diaglog... Thu Dec 5 14:42:47.209 [initandlisten] shutdown: going to close sockets... Thu Dec 5 14:42:47.209 [initandlisten] shutdown: waiting for fs preallocator... Thu Dec 5 14:42:47.209 [initandlisten] shutdown: closing all files... Thu Dec 5 14:42:47.209 [initandlisten] closeAllFiles() finished Thu Dec 5 14:42:47.209 dbexit: really exiting now
Note: MongoDBs data files are usually located at /data/db but in my Ubuntu installation they where in /var/lib/mongodb.
Repair preserving data:
sudo mkdir /var/lib/mongodb0 sudo mongod --dbpath /var/lib/mongodb --repair --repairpath /var/lib/mongodb0 sudo mongod --dbpath /var/lib/mongodb0
Now that the server is up with a repaired version (/var/lib/mongodb0) of your original data (from /var/lib/mongodb) use mongo client to verify that everything is OK. In that case replace /var/lib/mongodb with /var/lib/mongodb0.
sudo rm -rf /var/lib/mongodb sudo mv /var/lib/mongodb0 /var/lib/mongodb sudo chown -R mongodb:mongodb /var/lib/mongodb
Repair without preserving data:
sudo rm /var/lib/mongodb/mongod.lock sudo mongod --dbpath /var/lib/mongodb --repair
When this completes, the repaired data files will replace the original data files in the /var/lib/mongodb directory.
Ref: http://docs.mongodb.org/manual/tutorial/recover-data-following-unexpected-shutdown/