Re: Installing grub to raw image

[Andrei Borzenkov]

07.10.2015 05:32, Jeremy Davis пишет:
> Hi,
>
> I am trying to install grub to a raw image (i.e. a flat file that will
> be used to house a VM). Host & guest image both Debian Jessie
>
> I have partitioned the file:
> part 1 : ext2 (for boot)
> part 2 : LVM (for root & swap)
>
> I have the raw mounted to /dev/loop0 with kpartx so these partitions map to:
>
> part 1 : /dev/mapper/loop0p1
> part 2 : /dev/mapper/loop0p2

I can reproduce something similar using grub2 in openSUSE Tumbleweed 
(2.02~beta2 with selected patches). The problem is that grub fails to 
detect that /dev/mapper/loop0p1 is partition of /dev/loop0 and so it 
does not include partition driver. The UUID in my case was correct (that 
of the first partition), but grub simply could not access it.

Current upstream seems to work for me in this configuration. You may 
want to test if it works for you.

> The LVM setup (vg labelled "lv")on part 2 provides:
> /dev/mapper/lv-root
> /dev/mapper/lv-swap_1
>
> I then have it mounted like this:
>
> /dev/mapper/lv-root -> /mnt
> /dev/mapper/loop0p1 -> /mnt/boot
>
> I then install grub like this:
>
> devicemap=/mnt/boot/grub/device.map
> chroot /mnt grub-mkdevicemap
> chroot /mnt grub-mkconfig -o /boot/grub/grub.cfg
> grub-install --force --grub-mkdevicemap=$devicemap --root-directory=/mnt
> /dev/loop0

--grub-mkdevicemap is a) no-op, it is accepted for legacy reasons only 
and b) you are using it incorrectly anyway, it pointed to a program to 
rebuild device.map, not to device.map itself.

> Which appears to install as it should:
>
> # chroot /mnt grub-mkdevicemap
> # chroot /mnt grub-mkconfig -o /boot/grub/grub.cfg
> Generating grub configuration file ...
> Found linux image: /boot/vmlinuz-3.16.0-4-amd64
> Found initrd image: /boot/initrd.img-3.16.0-4-amd64
> done
> # grub-install --force --grub-mkdevicemap=$devicemap
> --root-directory=/mnt /dev/loop0
> Installing for i386-pc platform.
> Installation finished. No error reported.
>
> (note that both systems are 64 bit so maybe this is the issue? But i
> doubt it as the host has the same info...)
>
> So this appears to all complete fine...
>
> But when I boot the raw image I get an error about a device not found (a
> UUID that I have no idea where it comes from. It does not appear to
> match any of the UUIDs that I see in the grub.cfg so I have no idea
> where this is coming from!?)
>
> I can fix grub easy enough from the vm:
> -boot with live iso
> -mount /dev/mapper/lv-root as /mnt & /dev/sda1 as /mnt/boot
> # grub-install --root-directory=/mnt /dev/sda
>
> Once grub is repaired than all works as it should, however I want it to
> just work from the start...
>
>  From looking around inside the (unbootable) raw it just looks like grub
> wasn't installed properly...
>
> # ls -l /mnt/grub
> total 2363
> -rw-r--r-- 1 root root      50 Oct  7 01:47 device.map
> -r--r--r-- 1 root root    5657 Oct  7 01:47 grub.cfg
> -rw-r--r-- 1 root root 2400500 Oct  6 10:18 unicode.pf2

Yes, it looks like grub installed somewhere else. You may want to run 
grub-install --debug ... to see what it did.

> Nothing like (working) /boot/grub on the host:
>
> # ls -l /boot/grub
> total 2380
> drwxr-xr-x 2 root root    4096 Aug 31 01:01 fonts
> -r--r--r-- 1 root root    7882 Oct  7 00:52 grub.cfg
> -rw-r--r-- 1 root root    1024 Aug 31 01:01 grubenv
> drwxr-xr-x 2 root root   12288 Oct  7 00:56 i386-pc
> drwxr-xr-x 2 root root    4096 Aug 31 01:01 locale
> -rw-r--r-- 1 root root 2400500 Aug 13 13:08 unicode.pf2
>
> FWIW the fixed /boot/grub dir looks the same as the host...
>
> Any help/guidance/insight/etc warmly welcomed!
>
> Regards,
> Jeremy Davis
>
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