pre-lock — Notification of a path lock attempt.
The pre-lock hook runs whenever
someone attempts to lock a path. It can be used to prevent
locks altogether or to create a more complex policy
specifying exactly which users are allowed to lock
particular paths. If the hook notices a preexisting lock,
it can also decide whether a user is allowed
to “steal” the existing lock.
If the pre-lock hook program returns
a nonzero exit value, the lock action is aborted and
anything printed to stderr is marshalled back to the
client.