Fixing MongoDB against unclean shutdown

It’s been a while since I maintained one of my servers that host an old project. After I got an HTTP 500 in an occasional case, I logged in to check what happened, only to find MongoDB is down. Running service mongod restart does not work. The MongoDB log indicates “Unclean shutdown detected.”

After a search on Google, here’s what I did to fix that:

# grep dbpath /etc/mongod.conf
# rm /var/lib/mongo/mongod.lock
# mongod --repair --dbpath /var/lib/mongo

At this point, you will see that MongoDB is running the repair process. If you immediately start MongoDB server after that, it still fails, because some permissions in /var/lib/mongo have been changed. You have to recover owner and group of those files back to “mongod” and then start the service:

# chown -R mongod:mongod /var/lib/mongo
# service mongod restart

Finally note that this is an CentOS server. If you use MongoDB on Ubuntu, some namings may be different.