mongodb service is not starting up
Solution 1:
On my ubuntu server, just run:
sudo rm /var/lib/mongodb/mongod.lock
mongod --repair
sudo service mongodb start
Solution 2:
Fixed!
The reason was the dbpath variable in /etc/mongodb.conf.
Previously, I was using mongodb 1.8, where the default value for dbpath was /data/db.
The upstart job mongodb(which comes with mongodb-10gen package) invokes the mongod with --config /etc/mongodb.conf option.
As a solution, I only had to change the owner of the /data/db directory recursively.