On Sat 24 Jan 2026 at 13:42:26 (-0700), D. R. Evans wrote:
> The documentation said:
>
> > # Inspect the current prefix (and other preset variables):
> > set
> > # Find out which devices are available:
> > ls
> > # Set to the correct value, which might be something like this:
> > set prefix=(hd0,1)/grub
> > set root=(hd0,1)
> > insmod normal
> > normal
>
> Saying "set to the correct value, which might be something like" leaves me
> just shaking my head, and not having any idea what I'm actually supposed to
> type.
>
> If I try to boot from the RAID disk, which drops me into grub rescue, then
> type "ls", it responds with:
> (hd0) (fd0)
>
> If I type "set", it responds with:
> prefix='(hd0)/BOOT/debain@/grub'
> root='hd0'
>
> which is basically a pair of magic incantations to me.
From my notes:
set root=(disk⁰,part¹)
sets the partition that a filename starting with / will use.
The superscripts give the lowest available number.
set prefix=(disk,part)
or
set prefix=($root)/boot/grub
specifies where Grub loads its modules from.
The Grub rescue> prompt has only four commands: insmod ls set unset,
so the aim is to find that $prefix directory, wherever it is.
I don't remember whether you will have tab completion. Type:
set root=(
and press TAB to find out. Otherwise, you have to use ls at each step
(dev by dev, dir by dir) until you find the grub directory.
Once the prefix is set correctly, type:
insmod normal
and then:
normal
whereupon the rest of Grub's commands should work.
Note that Grub's "root" has nothing to do with the root=UUID=1234…
that's handed to the kernel for finding the root filesystem.
> When I used a couple of seemingly-well-regarded rescue disks that are supposed
> to make this easy (supergrub2 and rescatux), before I posted the problem on
> the reflector, they both complained about unknown filesystems on the disk and
> wouldn't let me do anything useful. That was the point at which I knew I
> needed help.
I have no experience with RAID. Perhaps there are other modules that
need loading, like mdraid09, mdraid09_be and mdraid1x.mod (which happen
to have 'raid' in their names). IDK, just guessing.
Cheers,
David.
