Bug#597084: grub-pc: /etc/kernel/postinst.d/zz-update-grub fails inside openvz chroot

[Michael Prokop]

Package: grub-pc
Version: 1.98+20100804-4
Severity: important


Installing a kernel inside a openvz guest chroot fails with:

[....]
Setting up linux-image-2.6.35-grml64 (grml.00) ...
Running depmod.
Examining /etc/kernel/postinst.d.
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 2.6.35-grml64 /boot/vmlinuz-2.6.35-grml64
update-initramfs: Generating /boot/initrd.img-2.6.35-grml64
[...]
run-parts: executing /etc/kernel/postinst.d/zz-update-grub 2.6.35-grml64 /boot/vmlinuz-2.6.35-grml64
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 1
Failed to process /etc/kernel/postinst.d at /var/lib/dpkg/info/linux-image-2.6.35-grml64.postinst line 346, <STDIN> line 2.
[...]

It's due to the failing update-grub command in
/etc/kernel/postinst.d/zz-update-grub:

  # update-grub
  /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

It fails because of the way openvz guests look like (simfs as
rootfs):

  # /usr/sbin/grub-probe --target=device /
  /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

  # cat /proc/self/mounts
  none /proc proc rw 0 0
  none /sys sysfs rw 0 0
  simfs /dev simfs rw 0 0

It works fine inside a KVM guest chroot which doesn't use the simfs
as rootfs:

  # /usr/sbin/grub-probe --target=device /
  /dev/vda1

  # cat /proc/self/mounts
  rootfs / rootfs rw 0 0
  none /sys sysfs rw,nosuid,nodev,noexec 0 0
  none /proc proc rw,nosuid,nodev,noexec 0 0
  udev /dev tmpfs rw,size=10240k,mode=755 0 0
  none /dev/pts devpts rw,nosuid,noexec,mode=600,ptmxmode=000 0 0
  /dev/disk/by-uuid/2bd80bd3-528c-431b-8b4a-47ecd1e27e24 / ext3 rw,errors=remount-ro,data=ordered 0 0
  [...]

  # readlink -f /dev/disk/by-uuid/2bd80bd3-528c-431b-8b4a-47ecd1e27e24
  /dev/vda1

I brought up a related issue on the grub mailinglist ~9 months ago:
"execution of update-grub in chroots might fail" ->
http://www.mail-archive.com/grub-devel@gnu.org/msg14328.html

And related as well (but not 100% similar) is issue #538118.
If you need further information, testing,... I'd be happy to help
out.

regards,
-mika-