Re: Grub rescue

[David WE Roberts]

On Tue, 26 Mar 2013 11:46:41 +0000, David WE Roberts wrote:

> On Sun, 24 Mar 2013 23:47:24 +0400, Andrey Borzenkov wrote:
> 
>> В Sun, 24 Mar 2013 16:58:55 +0000 (UTC)
>> David WE Roberts <address@hidden> пишет:
>> 
>>> On Sun, 24 Mar 2013 16:14:48 +0000, David WE Roberts wrote:
>>> 
>>> > Should grub rescue started from an MBR disc be able to see GPT
>>> > partitions?
> 
> <snip>
> 
>> If you still can boot in original configuration, reinstall grub while
>> explicitly adding part_gpt:
>> 
>> grub-install --modules=part_gpt ...
>> 
>> If you cannot return to original configuration - just follow boot
>> recovery procedure for your distro.
> 
> Done that.
> 
> When I disconnect the original MBR data drive and connect the new GPT
> data drive and boot grub of the MBR disc and go into grub rescue
> 
> I still find that 'ls' can only see one drive, the one with the MSDOS
> partitions on.
> 
> If I 'insmod part_gpt' it does not complain, but still can't see the GPT
> drive.
> 
> Not enough in core.img to chain load Windows either.

Test #2

Boot from Ubuntu 12.04 Live CD into 'Try'

startup Terminal

sudo bash

mount /dev/sdb2/ /mnt/

[ls to confirm correct filestore mounted]

grub-install --boot-directory=/mnt/boot /dev/sda

reboot, and get

error: no such device: 28ba1903-0731-40e2*8ce2-55e5597293c2

 >set

prefix=(hd0,2)/boot/grub

root=hd0,2

>ls

(hd0)


So as far as I can see grub-install has installed grub on /dev/sda and set 
up core.img to cope with a GPT disc and correctly identified the disc and 
that /boot/grub and /root are on partition 2 of the disc.

When the initial bit of grub starts to load, it is unable to see the GPT 
disc (no such device:) and reverts to the only disc it can see, the MBR 
disc.

However it hasn't got the module 'part_msdos' included so it can't even 
see the partitions on the MBR disc.

[I checked this - at the grub rescue> prompt insmode part_gpt worked, 
insmod part_msdos failed.]

So I think this is a bug not a feature.

It looks as though currently the only way that I can get my GPT disc up 
and running using grub2 from an MBR disc is to have /boot/grub in a 
separate mini-partition on the MBR disc. Assuming even that works.

I will try a full install of Ubuntu 12.04 onto the GPT disc, nominating 
the MBR disc as the location for grub, and see what happens.
However I fully expect the same failure.

Bug: grub 2 on initial boot does not correctly support GPT discs with the 
module 'part_gpt'.
It fails to recognise the disc or the partitions.

Note that the discs are configured in AHCI mode.

Regards

Dave R