Comment 27 for bug 1012629

I still find issues installing grub via 'd-i grub/installer' if there are more than one disk. Or it could be the other issue Dave Chiluk referred to in the post #23.

Tried this on Precise (12.04.4, 12.04.5) and Trusty with errors.

d-i debconf/priority string critical
d-i partman/early_command string debconf-set partman-auto/disk "/dev/sdb"
# My partition recipe
d-i grub-installer/only_debian boolean false
d-i grub-installer/with_other_os boolean false
d-i grub-installer/bootdev "/dev/sdb"

I see the update grub run but ubuntu never boots after the install.

I could only workaround these issues via a late_command to run the grub-install from the target itself via chroot.