I've just realised that these messages appear at all because the log priority is low enough that they appear, booting with "--quiet" on the kernel command-line is enough to hide them. But we use "quiet" not "--quiet", Upstart should respect that
I've just realised that these messages appear at all because the log priority is low enough that they appear, booting with "--quiet" on the kernel command-line is enough to hide them. But we use "quiet" not "--quiet", Upstart should respect that