Most likely the problem was simply that grub was not installed to the MBR and you just needed to run a dpkg-reconfigure grub-pc to make sure sda was selected. Since you have resolved the problem, I'm closing the bug.
** Changed in: grub2 (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1051280 Title: reboot into grub prompt after system update To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1051280/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs