About MongoDB lock file (mongodb.lock)

the mongodb.lock file is a simple file which holds a random number and it is doing
most important tasks for MongoDB

Important of mongodb.lock file

1. To detect unexpected/ Unclean shutdown

2. dbpath only access by ONE mongod process


If you have seen any unexpected shutdown or hanged MongoDB server you have to repair your MongoDB before it starts.

Here are basic steps

1. look at the mongodb log file and see bottom lines of log. You will see some clue on mongod hanged
    tail -n 20 /var/log/mongodb/mongodb.log
    you  may see below error message
    "Detected unclean shutdown - mongod.lock is not empty."

2. Create a backup copy of the data files in the --dbpath.
    mongodump --dbpath /data/mongodb/ -o /var

3. Start mongodb with --repair command
    mongod --dbpath /data/db --repair

After the repair, the dbpath should contain the repaired data files and an empty mongod.lock file.