How to use fsyncLock() safely in backing up a single mongod

I read from mongodb document:

important:
db.fsyncLock() may block reads, including those necessary to verify authentication
warning:
When calling db.fsyncLock(), ensure that the connection is kept open to allow a subsequent call to db.fsyncUnlock(). Closing the connection may make it difficult to release the lock.

In worst case, I use fsyncLock() to block database and suddenly lost connection to database (because of temporary network failure). I cannot reconnect because fsyncLock() block reader. My database will be blocked forever.

I am considering to shutdown mongodb to backup.

What is the most safest backup solution for single mongod ?