[lug] Grub Install

[Zan Lynx]

On Tue, 2007-01-30 at 10:59 -0700, David Morris wrote:
> On Tue, Jan 30, 2007 at 10:12:31AM -0700, Lee Woodworth wrote:
[snip]
> > Grub is also sensitive to device enumeration order. As
> > long as the bootable devices are constantly plugged in
> > things can work. External SCSI devices that may or may not
> > be powered up would complicate things.

Wait a sec here.  Grub uses the BIOS disk order.  So for Grub it is the
interaction with the system BIOS, the SCSI controller BIOS, etc, that
determines the drive numbers.

That /boot/grub/device.map file is how Grub determines what the first
BIOS disk is supposed to be.  hd0 is supposed to be BIOS boot disk, hd1
is the next one, etc.

Now, if you have a SCSI controller with external drives, *AND* those
external drives are listed in controller BIOS as bootable, *AND* they
are sometimes on, sometimes off, *then* you will have boot order
problems.

Or if you have your BIOS set to boot removable drives, CD drives or
floppy drives first, that would be another problem.

There are two times *kernel* device ordering will mess up the Grub boot.
One is in the command line passed by Grub to the kernel.  If it
specifies /dev/sda1 as the root filesystem, and the kernel puts a USB
drive on /dev/sda, then the kernel won't boot.  The other time is if you
run grub-install twice and Grub's device.map file should have changed
(because sda is now sdc) but didn't.  grub-install only generates a
device.map file one time unless you tell it to rescan.

The modern fix for the root device is is a initrd or initramfs that
contains a mini-udev, and then the kernel command line can specify the
root filesystem by label or UUID or whatever.
-- 
Zan Lynx <zlynx at acm.org>
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