pre-unlock — Notification of a path unlock attempt.
The pre-unlock hook runs whenever someone attempts to remove a lock on a file. It can be used to create policies that specify which users are allowed to unlock particular paths. It's particularly important for determining policies about lock breakage. If user A locks a file, is user B allowed to break the lock? What if the lock is more than a week old? These sorts of things can be decided and enforced by the hook.
If the pre-unlock hook program returns a non-zero exit value, the unlock action is aborted and anything printed to stderr is marshalled back to the client.