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.