Re: Problems with grub2/initramfs-tools in chroot
On 21/11/14 15:13, Ross Boylan wrote:
> Over the last week I've repeatedly found my machine unbootable, in the
> sense I couldn't get to a working system without intervention.
> Sometimes I couldn't even get the grub2 menu.
Tick
>
> Things are OK now, but I'm trying to understand what went wrong so I
> don't do it again.
>
> I had multiple disks and was working on the first 2. Initially I
> worked on sdb and left sda blank.
Tick
> My setup involves various extras:
> software RAID, crypo (cryptsetup) and LVM, though not all system
> instances used all those. Disks were GPT (or blank); everything was
> wheezy amd64.
>
> I would install a system using debootstrap following Appendix D of the
> installation manual. I bind mounted /dev and /dev/pts, and usually
> /sys and /proc to the chroot before switching to it. I usually ran
> the grub setup from within the chroot.
>
> It's not clear to me exactly what is going on running grub-install
> from a chroot. Because of the bind mounts I assume it has access to
> the devices so that grub-install /dev/sdb actually installs to sdb.
> But the chroot simply has a file system without knowing how it was
> mounted. The chroot might not even have the packages to deal with its
> filesystem (e.g., a chroot run on an encrypted LVM volume on top of
> RAID need not have mdadm, cryptsetup, or lvm2 installed---not just in
> theory but in my practice).
>
> initramfs-tools tries to figure out what modules should be in the
> initrd, but it's not clear to me how it decides (consulting fstab,
> mdadm.conf and related files? install a module if the relevant
> package is installed? call the OS? consult /proc?). I think this led
> to some problems, e.g., the chroot was on a /dev/mdx, but the mdadm
> tools did not end up in the initrd.
>
> Eventually I created a system on sda and ran grub-install /dev/sda from
> inside the chroot. Not only did the system not boot off sda, when I
> told it to prefer booting off sdb I didn't get back what I had before;
> instead I got an older setup for sdb.
Tick
>
> Could changing the boot order in the BIOS change the drive mappings
> and screw up grub that way?
Yes.
>
> Thanks for any wisdom.
>
> Ross Boylan
>
> P.S. When formatted, both disks got a bios_grub partition.
I've had a 'similar' problem, in my case it was solved with:-
grub-install /dev/$Whatever
If the problem is GRUB, and you are actually booting from sdb (due to
the BIOS settings making it the boot device.
Note: double check device names (you can use the GRUB device name) with
the mount command and use SMART to determine which device it the one set
to boot from in the BIOS.
Hope that helps.
Kind regards
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