UPDATE: in the end I just rebooted from command line (not the AWS console), without removing grub from the disk or the partition, and it worked fine. I'm not sure whether AWS is even using this virtual disk in the boot process.
Output from update-grub is: Sourcing file `/etc/default/grub' Sourcing file `/etc/default/grub.d/50-cloudimg-settings.cfg' Generating grub configuration file ... Found linux image: /boot/vmlinuz-4.15.0-1056-aws Found initrd image: /boot/initrd.img-4.15.0-1056-aws Found linux image: /boot/vmlinuz-4.15.0-1054-aws Found initrd image: /boot/initrd.img-4.15.0-1054-aws Found linux image: /boot/vmlinuz-4.15.0-1044-aws Found initrd image: /boot/initrd.img-4.15.0-1044-aws done -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/751057 Title: grub-pc upgrade on Amazon EC2: The GRUB boot loader was previously installed to a disk that is no longer present, or whose unique identifier has changed for some reason. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-on-ec2/+bug/751057/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
