Mandatory locking

Mandatory locking is enforced by the kernel

Doesn't rely on processes checking for locks.

Occur automatically when a program uses flock(), lockf(), or fcntl().

If a program puts a 'read' or 'shared' lock on a file, no other processes can write to it .

If a program puts a 'write' or 'exclusive' lock on a file, no other processes can read or write to it.