A few days ago I had a problem where mongodb crashed and I couldn't start it up. I realized that this problem occurred because the disk was full. So I
rm -rf a few things and try to
sudo service mongod start . But this wasn't successful. I googled this problem and I quickly found the solution:
sudo rm /var/lib/mongodb/mongod.lock sudo mongod --repair sudo service mongodb start
After this mongodb started without any problems.