Re: Use grub-rescue on a non-bootable RAID-formatted drive [WAS: Re: status: how to install grub to non-bootable RAID-formatted drive?]
On Thu 29 Jan 2026 at 16:59:37 (-0700), D. R. Evans wrote:
> D. R. Evans wrote on 1/29/26 4:53 PM:
> > David wrote on 1/29/26 3:55 PM:
> >
> > > to read in the root directory of each device in turn. Can you please
> > > report the result of these interactive grub-rescue commands, after booting
> > > your system with only the drive being rescued connnected:
> > >
> > > ls (hd0)/
> > > ls (hd0, msdos1)/
> > > ls (hd0, msdos2)/
> > > ls (md/0)/
> > >
> >
> > They all return:
> > error: unknown filesystem
>
> FWIW (which may be nothing), when I used a couple of GRUB rescue disks
> before first posting here, they both trundled and thought for a bit,
> then errored out with a similar message.
That's worrying. A Grub rescue prompt could well fail because it needs
modules to read the filesystems, but needs to read the filesystems to
find its modules, which is why it needs a human to help it search
every nook and cranny of all the devices for some modules to load.
But a Grub Rescue disk should be complete and need no modules from
elsewhere.
I wondered, knowing nothing about RAID, whether the partition has some
metadata at the start, before the actual ext4 (or whatever) filesystem
starts. I don't even know whether Grub has the ability to look at
partitions in that way. You've examined this disk when another disk is
booted in the machine, haven't you? I don't know whether there are
mdadm options to list these sorts of parameters.
Cheers,
David.
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