Comment 21 for bug 1928674

Bionic: server install from ubuntu-18.04.5-live-server-amd64.iso. Security updates applied by subiquity, including grub-efi-amd64 2.04-1ubuntu44. /etc/kernel/post{inst,rm}.d/zz-update-grub are not present (to my surprise - then I worked out this was because grub wasn't installed in the source squashfs, so this was a new install of the package from -security rather than an upgrade).

grub-pc is not installed.

Enabled -proposed in sources.list.

sudo apt install grub-efi-amd64 grub-efi-amd64-bin grub-efi-amd64-signed

/etc/kernel/post{inst,rm}.d/zz-update-grub now exist as expected

sudo apt dist-upgrade to install 4.15.0-144-generic kernel from bionic-proposed (along with other random bits)

Inspecting /boot/grub/grub.cfg shows references to -144-.

Rebooting, and uname shows -144- is booted.

Disabled -proposed again.

sudo do-release-upgrade to focal, to my surprise, does not fail with conffile conflicts when -proposed is disabled. However, it does fail to upgrade grub-efi-amd64* due to focal-updates having an earlier version than bionic-proposed.

$ dpkg -S /etc/kernel/postinst.d/zz-update-grub
grub2-common: /etc/kernel/postinst.d/zz-update-grub
$

I do not understand what's happening here with the silent takeover of the conffiles without an explicit Replaces allowing this; this is not how I understood dpkg to behave.

I think this is verification-done for bionic and verification-failed for grub2 in focal (which should be withdrawn).
I do not understand what's happening with the conffile being