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Unlocks a mongod instance to allow writes and reverses the operation of a db.fsyncLock() operation. Typically you will use db.fsyncUnlock() following a database backup operation.

db.fsyncUnlock() is an administrative operation.

Compatibility with WiredTiger

Changed in version MongoDB: 3.2

db.fsyncLock() ensures that the data files are safe to copy using low-level backup utilities such as cp, scp, or tar. A mongod started using the copied files contains user-written data that is indistinguishable from the user-written data on the locked mongod.

Prior to MongoDB 3.2, db.fsyncLock() cannot guarantee that WiredTiger data files are safe to copy using low-level backup utilities.

The data files of a locked mongod may change due to operations such as journaling syncs or WiredTiger snapshots. While this has no affect on the logical data (e.g. data accessed by clients), some backup utilities may detect these changes and emit warnings or fail with errors. For more information on MongoDB- recommended backup utilities and procedures, see MongoDB Backup Methods.