Subject: Re: Reboot Command and Firmware Settings
To: Curt Sampson <email@example.com>
From: Chris G. Demetriou <firstname.lastname@example.org>
Date: 05/01/1997 13:26:57
> My firmware is set to boot from dka0 by default, and this works
> fine. However, I've noticed that if I boot of my emergency root on
> dka100 and then use NetBSD `reboot' rather than NetBSD `halt' and
> firmware `boot', the reboot happens from dka100 rather than dka0.
> Should this really be happening? I personally would find it more
> convenient to use the firmware defaults for the reboot command.
"Tell that to the firmware engineers."
The reboot process is something like:
The running kernel tells the firmware that's it's time to
The firmware loads the boot blocks, and tells it which
device, kernel, flags, etc. to load.
The boot blocks load whatever the firmware said.
Note that the running kernel, or anything else other than previous use
of the firmware, does not communicate which device to boot from, etc.,
to the firmware.
There's specific wording that states how this is all supposed to work
in the Green Book. It actually varies from system to system, because
of firmware bugs/problems/whatever.
But, in a nutshell, there's nothing that the running kernel does to
tell the firmware what to boot from, and little that it _can_ do; the
firmware decides for itself, based on the existing firmware
environment variables and the previously-booted device/kernel.