Comment 61 for bug 1527727

From the install log you can see that we install grub2 at 2.02~beta2-36ubuntu3.17.
   ..
   Unpacking grub2-common (2.02~beta2-36ubuntu3.17)
   ..

'dpkg-reconfigure grub-pc' and 'grub-install /dev/vda' are run

And also:

  run-parts: executing /etc/kernel/postinst.d/zz-update-grub 4.4.0-116-generic /boot/vmlinuz-4.4.0-116-generic
  Generating grub configuration file ...
  Found linux image: /boot/vmlinuz-4.4.0-9025-euclid
  Found initrd image: /boot/initrd.img-4.4.0-9025-euclid
  Found linux image: /boot/vmlinuz-4.4.0-116-generic
  Found initrd image: /boot/initrd.img-4.4.0-116-generic
    /run/lvm/lvmetad.socket: connect failed: No such file or directory

Then during boot we see

[ 0.000000] Command line: BOOT_IMAGE=/ROOT/zfsroot@/boot/vmlinuz-4.4.0-9025-euclid root=ZFS=rpool/ROOT/zfsroot ro console=ttyS0

So we have successfully booted from root on a zfs system.