启动mongodb遇到的一个问题和解决：
转（http://blog.csdn.net/u012877472/article/details/51001025）
MongoDB: exception in initAndListen: 20 Attempted to create a lock file on a read-only directory: /data/db, terminating
sudo chmod -R go+w /data/db or this, which will make the directory owned by you: sudo chown -R $USER /data/db