start-commit — Notification of the beginning of a commit.
The start-commit hook is run before the commit transaction is even created. It is typically used to decide if the user has commit privileges at all.
If the start-commit hook program returns a non-zero exit value, the commit is stopped before the commit transaction is even created, and anything printed to stderr is marshalled back to the client.
The command-line arguments passed to the hook program, in order, are:
authenticated username attempting the commit