Re: GRUB only offers a rescue shell

[Pascal Hambourg]

Le 13/07/2017 à 21:12, Jordan Uggla a écrit :
> On Wed, Jul 12, 2017 at 9:09 AM, Hao Lee <address@hidden> wrote:
> > 3. Attach the whole image to /dev/loop0 and attach the first partition
> > to /dev/loop1
> >
> > sudo losetup /dev/loop0 hd.img
>
> You're fine up to here.
>
> > sudo losetup -o $((2048*512)) /dev/loop1 hd.img
>
> This is where your problem is. When you run grub-install it detects
> two disks, /dev/loop0 and /dev/loop1 where /dev/loop0 appears to be a
> partitioned disk with none of its partitions mounted and /dev/loop1
> appears to be a disk without any partition table where the whole disk
> is mounted to /mnt/.

Agreed.

> Instead, you should run "sudo kpartx -a /dev/loop0" which will probe
> the partition table of /dev/loop0 and add device nodes in /dev/mapper/
> for each of the partitions found. In this case, it would create a
> device node /dev/mapper/loop0p1 . When grub-probe looks at
> /dev/mapper/loop0p1 it will be able to detect that it is a partition
> of the disk /dev/loop0 and thus grub-install will configure things
> appropriately.

I did not think that grub-install was able to detect that a /dev/mapper 
device was actually a partition of another device.

An alternative method is to make the kernel aware that the loop device 
is partitioned by loading the loop module with the max_part= option or 
adding the -P/--partscan option to losetup.

> That is because grub-install detected that /boot/grub/ was on a "disk"
> with no partition table, and thus didn't include the part_msdos module
> in the core.img. Again, the solution to that problem is described
> above.

Or one could force grub-install to include the part_msdos module in the 
core image with the --modules=part_msdos option.