Comment 12 for bug 1635181

As an update to this:

I think we agreed (in a short meeting between people involved in curtin, cloud-init, grub2, etc.) that installers are indeed meant to be authoritative on writing /etc/default/grub.

One work item that came out of this was to at the very least make it clear what files are being used to generate grub.cfg. I've uploaded this to Disco already:

https://launchpad.net/ubuntu/+source/grub2/2.02+dfsg1-5ubuntu9

The same fixes are also being prepared for SRU in 18.04 and 18.10 (they should be available in -proposed incessantly).

I opened bug 1812863 since I didn't know this one was here -- regardless, there'd still be the question of handling config merging when grub2 expects to have distro-wide defaults, installers write their own things, and on top of that users might want to make configuration changes. This is still an issue we'll have to handle when curtin/cloud-init do write to /etc/default/grub directly, so this here bug can remain open with a grub2 task to denote the work that is needed there. We've already started looking into how to handle it, too.

For the time being, running 'update-grub' will provide additional information on what files are being sourced to generate the final grub.cfg configuration file that lands in /boot/grub/grub.cfg:

$ sudo update-grub
[sudo] password for mtrudel:
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/50-curtin-settings.cfg'
Generating grub configuration file ...
[...]
done