Re: In a multiboot context (2 Ubuntu and 2 Windows OSes), Grub shows a very surprising behavior. Is this a bug ?

[Jordan Uggla]

On Fri, Mar 30, 2012 at 8:13 AM, Arbiel Perlacremaz
<address@hidden> wrote:
> Hi
>
> This call for help is related to an issue raised on the Ubuntu.fr forum.

I'm unable to access http://forum.ubuntu-fr.org/post.php?tid=860661 ,
I get the error "Vous n'êtes pas autorisé(e) à afficher cette page."
which I assume means that I need to create an account and log in to
view the page. I'd personally prefer if you would post the boot info
script results here directly, and it will probably make things easier
for other people reading this thread as well.

> Even if you don't understand french, you will find there BootInfo reports,
> menuentry codes, ...  I can help translate any additionnal information you
> may fell necessary to understand.
>
> The situation is the following :
> three disk drives
> first drive : two Ubuntu 11.10 et 12.04
> second drive : Windows 7
> third drive : Windows 8.
>
> Grub sits on the MBR of each drive and, as long as we have been able to
> understand, each Grub instance points to a unique grub.cfg, which sits on
> drive 1.
>
> 4 menues entries (discarting the recovery and memory testing entries)
> Ubuntu 11.10
> Ubuntu 12.04
> Windows 7
> WIndows 8.
>
> Windows 7 menuentry boots Windows 8.
>
> This may be a Windows issue, however tests run by the user show a very
> surprising Grub's behavior.
>
> When the BIOS points to the second drive, the selection of  the Windows 7
> menuentry boots Windows 7. This is quite surprising as Grub sits on the MBR
> of this drive and uses the same grub.cfg file as the Grub which sits on
> drive 1. The only difference in the two runs seems to be the way grub names
> the drives. But even this does not explain the behavioral difference, as the
> "set root=(hdx,msdosy)" are followed by a "search --set=root" instruction
> before invoking the "chainloader" command.

Indeed, if your assessment is completely correct I would expect there
to be no behavioral difference.

>
> By the way, what is the purpose of the "set root=" commands ? They seem to

As far as I know they are for backward compatibility with older
versions of grub, and also serve as a fallback if for some reason the
search command fails but the partition/filesystem is still accessible
(though I can't think of any way that could happen off hand).

> me to be quite useless, unless ${root} is taken as a default value for the
> --hint option of the search command. And in that case, why not code the
> --hint option into the search command.
>
> Any explanation will be welcome.
>
> Arbiel
>
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-- 
Jordan Uggla (Jordan_U on irc.freenode.net)