Bug#1108204: initramfs-tools: update-initramfs trigger does not update the initramfs in some cases

[Tobias Graemer <tobias.graemer@mt.com>]

Package: initramfs-tools
Version: 0.148.2
Severity: normal

Dear Maintainer,

When installing a kernel package and a package with a trigger for update-initramfs
in one go, the update of the initramfs is skipped in some cases.

In a clean chroot, populated with debootstrap for "trixie", I ran

  apt install linux-image-amd64 plymouth-theme-mobian

Result:

  [...]
  Setting up linux-image-6.12.32-amd64 (6.12.32-1) ...
  I: /vmlinuz.old is now a symlink to boot/vmlinuz-6.12.32-amd64
  I: /initrd.img.old is now a symlink to boot/initrd.img-6.12.32-amd64
  I: /vmlinuz is now a symlink to boot/vmlinuz-6.12.32-amd64
  I: /initrd.img is now a symlink to boot/initrd.img-6.12.32-amd64
  /etc/kernel/postinst.d/initramfs-tools:
  update-initramfs: Generating /boot/initrd.img-6.12.32-amd64
  Setting up linux-image-amd64 (6.12.32-1) ...
  Setting up plymouth-theme-mobian (1.1) ...
  update-alternatives: using /usr/share/plymouth/themes/mobian/mobian.plymouth to provide /usr/share/plymouth/themes/default.plymouth (default.plymouth) in auto mode
  Processing triggers for libc-bin (2.41-8) ...
  Processing triggers for initramfs-tools (0.148.2) ...
  update-initramfs: /boot/initrd.img-6.12.32-amd64 has already been updated since Mon Jun 23 06:07:09 2025.
  #

The initramfs is updated after setup of the kernel package. It is NOT updated again
after setup of package plymouth-theme-mobian, which is wrong. The files that are
installed by package plymouth-theme-mobian are missing in the initramfs (and the
plymouth splash screen will not work).

This behaviour was introduced in version 0.147 by:

  [7f2ed35] Avoid updating the initramfs twice for some cases (LP: #1466965)

My use-case is that I install the kernel package and plymouth-theme-mobian
during an image build that runs in a debootstrap chroot.
I could work around the issue by manually calling "update-initramfs -u" at the
end of the image build, or by calling update-initramfs in the postinst script
of plymouth-theme-mobian (instead of defining a dpkg trigger). I consider both
ways as workarounds and the new behaviour of update-initrafms as a bug.

Note that I'm not a Mobian developer nor do I use that package. I have a custom
package that defines a trigger in the same way as plymouth-theme-mobian where I
observe the issue.

Tobias