Re: Grub rescue

[David WE Roberts]

On Tue, 26 Mar 2013 12:07:59 -0700, Jordan Uggla wrote:

> On Tue, Mar 26, 2013 at 6:50 AM, David WE Roberts
> <address@hidden> wrote:
>>
>> Test #3
>>
>> Installed Ubuntu 12.04 64 bit to the partition on the GPT drive where
>> it was previously installed.
>>
>> Nominated MBR drive as boot drive.
>>
>> Same failure as Test #2.
>>
>> Now, of course, I can't boot anything because when I revert back to a
>> full MBR configuration core.img is set up for GPT partitions so can't
>> see the MBR partitions, although it can see both MBR discs.
>>
>> About to rerun Test #2 on the MBR configuration to reset core.img (I
>> hope).
> 
> I am very confused about what you're trying to accomplish, and even more
> confused about what you've done up to this point. There is no reason
> that you should need to get stuck at a grub rescue shell when
> transitioning from an msdos label to a GPT label if you run grub-install
> properly (meaning, passing the device whose boot sector your BIOS is
> going to load, and if needed a proper --boot-directory argument, no
> --modules argument should ever be necessary) after making any
> partitioning changes. Please re-run grub-install (without --modules) and
> note down the exact command you ran, as well as the output of "mount"
> when you ran grub-install, and post both. If after that grub-install
> command you're still not able to boot, please run boot info script
> http://bootinfoscript.sourceforge.net/ from a LiveCD/USB or other
> working GNU/Linux installation and post the RESULTS.txt that it
> produces.

Will do.

However to me what I am doing is very simple.

I am booting grub from MBR on disc /dev/sda.

It is loading the main part of grub from /dev/sdb1 on MBR disc /dev/sdb.

/dev/sdb1 is an ext2 partition which is the root mount point for my Ubuntu 
filestore; /boot/grub is also on /dev/sdb1 as an integral part of the 
filestore.

All this works fine.

However I am moving my /dev/sdb from a 750GiB MBR drive to a 3GiB GPT 
drive.

Because of the extra partition automatically created at the start of a GPT 
drive the first useable partition on the GPT drive is /dev/sdb2.

So (in the simplest example) I am installing a brand new instance of Ubuntu 
12.04 64 bit on /dev/sdb2 which contains both the / (root) filestore and 
also /boot/grub.

I am still booting initially (first bits of grub) off MBR disc /dev/sda 
with the expectation that grub will be able to see /dev/sdb2 on the GPT 
disc and find /boot/grub with all the information it requires to complete 
booting.

I have assumed that this is what 'part_gpt' is supposed to do. i.e. it 
should be able to recognise a GPT disc, recognise the partitions within 
that disc, and then enable grub to access data from one of the partitions.

As I understand it this is what 'part_msdos' does with MBR discs.

The problem I have is that with 'part_gpt' in core.cfg grub cannot see any 
partitions (although it sees the MBR disc(s).

With both 'part_gpt' and 'part_msdos' in core.cfg grub can see the MBR 
discs and partitions but still cannot see the GPT disc - so obviously 
cannot see the GPT partitions either.

Bottom line - grub seems unable to recognise my GPT disc even when I have 
installed a new version of Ubuntu in an ext2 partition on the GPT disc and 
told it to put grub in the MBR of my MBR disc.

Regards

David