Bug#987377: rescue-mode: when in graphical mode, locks up one prompt before the shell

[Philip Hands <phil@hands.com>]

Package: rescue-mode
Version: 1.83
Severity: normal

Dear Maintainer,

When booting recent daily images, or the bullseye-DI-rc1, into "Graphcal rescue
mode", on a system with a simple partition for root, when one selects to enter a
shell it clears the screen in order to display the "intro" message, but then
fails to do so.

Instead it just sits there with a blank screen for a while that looks like this:

   https://openqa.debian.net/tests/1422#step/rescue/2

if one flips to tty3, chroots into the /target and runs htop, one sees that a
CPU is being kept completely busy by:

   debconf -o d-i /usr/bin/main-menu

If one edits the rescue-mode.postinst before getting to the rescue step, to
change the priority of the intro to low, thus:

  sed -i -e '/"rescue.*intro"/s/high/low/' /var/lib/dpkg/info/rescue-mode.postinst

then if doesn't try to show the problematic page, and thus gets to the shell.

This seems to prove that the issue is with debconf, rather than some problem
with mounting file systems or whatever.

This has been reporoduced under qemu (as seen above in the openQA test, and
under libvirt/quemu on my laptop) and also by booting an X230 thinkpad from USB
stick.

Cheers, Phil.