Re: how to install grub to non-bootable RAID-formatted drive?
On Thu, Jan 22, 2026 at 10:03:11AM -0700, D. R. Evans wrote:
> Due to a cascading series of failures (some of hardware, some of my brain),
> I find myself in the following situation:
You do not say what sort of RAID you are using, but you have 2 disks so I
assume RAID-1 (mirrored disks).
I also assume that you have a root file system that is a primary disk
partition, ie you do not use LVM.
The easiest way to recover is to boot from a bootable Debian USB memory stick
or CD-ROM. Do not try to rescue, do something like below - needs work at the
command line.
Boot the machine to give you a desktop.
Open a terminal, become root
Identify the hard disk that contains your system, look at /proc/partitions.
I am going to assume that it is /dev/sda with the root file system as /dev/sda1
mkdir /tmp/RFS
mount /dev/sda1 /tmp/RFS
Copy /dev/ to /tmp/RFS/dev/
chroot /tmp/RFS /usr/bin/bash
grub-install /dev/sda
sync
exit
reboot
The above just typed, not tested.
> I had a linux-raid two-drive system that was working fine for many years.
> The system uses legacy BIOS booting. My notes from long ago say that both
> drives had a working GRUB; but it seems that my notes were wrong: one of the
> drives died without warning, leaving me with a drive with a
> fully-functioning trixie (and all the user data, etc.) present, but that
> drive seems to have no working GRUB in the MBR. Trying to boot it gives me a
> "grub-rescue>" prompt.
>
> I've scoured the Internet, but have been unable to find any clear,
> unambiguous, step-by-step guide as to how to make this drive remaining
> functioning drive bootable, either from the "grub-rescue>" prompt or by some
> other mechanism. I tried a couple of rescue disks that I located on the
> Internet, but they both errored out when I attempted to "rescue" the drive.
> So I've given up, at least for now, on trying to fix the problem from the
> "grub-rescue>" prompt.
>
> I can physically remove the drive and place it on a functioning machine, and
> have done so. With the drive in the functioning machine, I have checked that
> indeed all the data on it (that were in the original "/" hierarchy) are
> readable. So I just want to find a way to install GRUB on the MBR in a way
> that will cause the disk to be bootable into the system that was on it. That
> is, I want to be able to remove the disk from the functioning machine that
> it's currently (temporarily) on, put the drive back in the original machine,
> power on, and have the system come up as it used to (except now with just
> one active drive in the RAID array).
>
> From there I can add a new drive to the array and get myself back a
> fully-functioning two-drive RAID-based system.
>
> I hope that that's a pretty clear description of the problem. If more
> information is needed, I can of course provide it.
>
> I hope that someone here understands all this GRUB-and-boot stuff better
> than I do, and can provide steps that my child-like brain can follow to get
> me back to a working system.
>
> Doc
>
> --
> Web: http://enginehousebooks.com/drevans
>
--
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256 https://www.phcomp.co.uk/
Parliament Hill Computers. Registration Information: https://www.phcomp.co.uk/Contact.html
#include <std_disclaimer.h>
Reply to: