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

From: Stefan Blachmann
Subject: Re: update-grub fails saying it cannot find a device for /
Date: Sun, 14 Nov 2021 16:20:54 +0100

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 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:

It basically says that I should use disk UUIDs instead of disk ids.
Now the problem is that grub-mkdevicemap does not make a
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/ 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 <> 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?

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