Migrate from aufs to overlayfs (Closes: #8415). This change touches
many components which won't all be listed individually, but some
highlights are listed below:
⋅ Adjust the build system to stop building the aufs kernel module.
⋅ Switch the kernel command line from union=aufs to union=overlayfs.
⋅ Adjust AppArmor profiles (Closes: #9045, #12112).
. Adapt chroot-browsers (Closes: #12105).
⋅ Drop the aufs Git submodule.
⋅ Make memory erasure feature compatible with overlayfs
(Closes: #15146).
⋅ Make Upgrader support and also generate overlayfs-based IUKs by
default (Closes: #9373).
Use GRUB with Secure Boot support for x86_64 (Closes: #6560, #15806).
This is also a large change, touching many components:
⋅ Install grub from bullseye.
⋅ Introduce a custom grub configuration file.
⋅ Use a custom background image.
⋅ Mimick Debian Installer's efi-image build script to handle all
dezerotracepen in binary local hooks.
⋅ Add SYSLINUX in the syslinux bootloader menu, to make it easier to
troubleshoot GRUB vs. syslinux issues (Closes: #17538).
⋅ Upgrader: Adjust to also handle files in EFI/debian when dealing
with file removals.
⋅ Adjust test suite.
Migrate test suite from Sikuli to a combination of OpenCV (image
matching), xdotool (mouse interaction), plus libvirt's send-key
(keyboard interaction) (Closes: #15460). This is another major
changes, allowing the test suite to run on Buster-based systems,
touching various areas of the test suite, among which:
⋅ Add workaround for the Greeter when restoring snapshot.
⋅ Fix dependencies for Buster.
⋅ Replace some Sikuli-based options with some OpenCV-based ones
(e.g. --retry-find → --image-bumping-mode).
⋅ Handle non-English keyboards.
⋅ Fix --capture on Buster and above.
⋅ Deal with Buster having migrated from avconv to ffmpeg.