Comment 49 for bug 1642298

Blake, your proposal makes sense on the surface; however, there are cases where it would cause problems. For instance, suppose that, outside of a MAAS environment, somebody installs Ubuntu, then installs Windows in a dual-boot configuration, then re-installs Ubuntu because Windows grabbed the boot process and the user couldn't figure out how to boot into Ubuntu. In this case, Ubuntu/GRUB would not then gain control of the boot process, which is what the user was hoping would happen, and (I THINK) what would happen today. Of course, re-installing Ubuntu was overkill in this scenario, and a little knowledge would go a long way to resolving the problem in an easier way; but I've seen posts on user forums from new users who do things like this. This isn't to say that your suggestion is a bad one; but implementing it would create some new problems of its own. They might be smaller than the ones we've got now, but they should be considered.

Three more points, should Blake's proposal be implemented:

First, and most importantly, the initial installation of GRUB in a MAAS environment would get it wrong, since as outlined, the proposal would give boot control to the local hard disk, which is exactly the problem we want to avoid. In such an environment, you'd need to install GRUB and ensure that it comes AFTER the PXE-boot option, otherwise the initial problem (MAAS losing control of nodes' boot process) would exist. Thus, either the GRUB package would need to take a cue from MAAS to leave the current top boot option in control (that is, install GRUB as the second or later boot option) or it would need enough smarts to figure this out itself. Given the wide variation in the way PXE-boot options appear in efibootmgr output, the former is likely to be more reliable than the latter.

Second, there's a potential implementation pitfall: There might be stale/invalid NVRAM entries that point to GRUB on non-existent devices. This could happen when MAAS redeploys a node, since the partition table will be wiped and new partitions created, but the NVRAM-based boot entries will be untouched. (Analogous things can happen in local/manual installations, too, of course.) The new EFI System Partition (ESP) will have a new GUID, which won't match the old one for the original installation. Thus, if the check for a reference to grubx64.efi doesn't include the GUID value (at a minimum; there are other identifying features, too), it might think the existing entry is valid, when in fact it's not. (Note that some, but not all, EFIs wipe invalid boot entries, so some computers might not exhibit this problem, but others will.)

Third, on systems that boot with Secure Boot active, the NVRAM entry will normally point to shimx64.efi, not grubx64.efi. In fact, this is usually the case even when Secure Boot is NOT active, or is unavailable; but with Secure Boot out of the picture, either binary should work to boot the computer.