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Re: GRUB (stuck on screen)

From: Jordan Uggla
Subject: Re: GRUB (stuck on screen)
Date: Sat, 5 May 2012 01:37:31 -0700

On Fri, May 4, 2012 at 2:32 AM, Peter Hillier-Brook <address@hidden> wrote:
> On 04/05/12 00:43, Jordan Uggla wrote:
>> On Mon, Apr 30, 2012 at 7:36 PM, Felix Miata<address@hidden>
>> wrote:
>>> not find the next part. Booting OM or USB sometimes can cause a
>>> dumb BIOS to reorganize device boot order, but proper Grub function
>>> depends on devices being found as and where they were when Grub was
>>> installed.
>> This is not true at all. GRUB2 makes no assumptions about drive
>> enumeration.
>> It is fairly common that users with multiple drives have two grub
>> boot sectors on two different drives, with one of those boot sectors
>> corresponding to a working grub version and the other corresponding
>> to an old grub installation which has since been broken. In this
>> case changing the boot priority in the BIOS can fix the problem by
>> getting the BIOS to boot from the drive with a grub boot sector
>> corresponding to the working grub installation (sometimes this can be
>> a different drive than that which contains /boot/grub/, which often
>> confuses people). So while changing the boot priority in the BIOS may
>> solve the problem, it wouldn't be for the reason you've given.
> Hello Jordan,
> you appear to have answered a question I raised on the Ubuntu list, namely
> why is someone modifying my BIOS by altering the boot order of my SATA
> disks.

You have misunderstood what I said. I said that changing the boot
priority in one's BIOS can sometimes solve boot problems, and gave an
example of a case where this might happen. The way that one changes
the boot priority in one's BIOS is through BIOS setup screens at boot,
and due to unstable device enumeration it may also change on its own
for no apparent reason. With BIOS based systems it is *impossible* for
GRUB, or any other software, to change the boot priority. With other
types of firmware like OpenFirmware and [U]EFI there are ways to do
this but there is no such interface defined for BIOS. Whatever you are
experiencing it is *not* anything being changed by GRUB or Ubuntu and
my guess would be that your BIOS simply does not have stable device
enumeration and its device enumeration affects boot device priority.

> I have Kubuntu on /dev/sdc and GRUB is installed thereon as my primary boot
> device. I also have Ubuntu on /dev/sdb with an historic installation of GRUB
> that is no longer used (os_prober does the job from /dev/sdc). After a
> dist-upgrade of Ubuntu on /dev/sdb my BIOS boot order is modified to point
> to /dev/sdb as the first device, causing the loss of what little hair I have
> left!
> This is not a desirable action and I would like to put an end to it,
> preferably permanently. Have you any advice?

I would recommend that you install grub's boot sector to the MBR of
all of your drives (and *no* partitions). That way your machine will
boot successfully no matter what drive your BIOS decides to boot from.
You will also need to configure Ubuntu's grub-pc package to do this
whenever the grub-pc package is upgraded. I don't currently know the
supported way to do the latter with Ubuntu 12.04.

Jordan Uggla (Jordan_U on

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