Re: update-grub fails saying it cannot find a device for /

[Stefan Blachmann]

No idea why grub-probe fails finding the / disk.

To make the update-grub script work, could it be a workaround to
replace grub-probe with a dummy script that just echoes "hd0,gpt4" or
such?

How does look a correct output when grub-probe does not fail?


On 11/14/21, Stefan Blachmann <sblachmann@gmail.com> wrote:
> Thank you for the quick reply, Andrei!
>
> I have mounted not only /dev, but also /sys, /proc and /run into the
> chroot, too. Didn't mention that to keep mail short.
>
> Meanwhile I found a possible hint:
> As there was no device.map file, I ran grub-mkdevicemap.
> This did no change again, update-grub still fails.
>
> Then, after a lot of searching the web, I found the second answer on
> this page might be a hint:
> https://serverfault.com/questions/401351/update-grub2-without-hardware-access-e-g-in-a-chroot
>
> It basically says that I should use disk UUIDs instead of disk ids.
> Now the problem is that grub-mkdevicemap does not make a device.map
> using UUIDs, it uses the IDs under /dev/disk/by-id.
>
> And I cannot add links to UUIDs as the answer on that page recommends.
> Because for reasons I do not understand, in /dev/disk/by-uuid I can
> see only the UUIDs of the *mounted* file systems (eg the live CD, and
> the ZFS boot and root filesystems), but of the drives themselves. I
> can not see UUIDs.
>
> When I manually change the /dev/disk/by-id/ device.map file entries to
> /dev/sda, sdb etc, there is no change in behaviour, update-grub still
> fails the same way.
>
> This is on Debian bullseye, which I assume uses GRUB 2.
>
> Any idea what could be done to make update-grub succeed?
>
>
>
> On 11/14/21, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>> On 14.11.2021 16:31, Stefan Blachmann wrote:
>>> When I enter
>>> # update-grub
>>> I get an error message:
>>> /usr/sbin/grub-probe: error: cannot find a device for / (is /dev
>>> mounted?).
>>>
>>> /dev has been mounted before entering the chroot /mnt environment using
>>> # mount --rbind /dev /mnt/dev
>>>
>>
>> In chroot you need at least /sys and /proc in addition to /dev, /run may
>> also be needed.
>>
>>> If I enter
>>> # grub-probe
>>> it answers:
>>> No path or device is specified.
>>>
>>> If I enter
>>> # grub-probe /boot
>>> it answers:
>>> zfs
>>>
>>> So, what do I need to do to make update-grub work?
>>>
>>
>>
>>
>