Bug#1108976: live-config: Graphical Live-System with Cinnamon fails to start properly under Trixie, works under Bookworm (regression)

[daniel.gestl@it-yourself.at]

Package: live-config
Version: 20250505 (Package live-build)
Severity: normal
X-Debbugs-Cc: <daniel.gestl@it-yourself.at>

Dear Debian Live team,

I would like to report a regression in the behavior of graphical Debian 
Live systems when built with live-build under Debian 13 (Trixie), 
compared to Debian 12 (Bookworm).

A graphical live system (using Cinnamon and LightDM) that was fully 
functional under Bookworm fails to start the graphical session under 
Trixie — even with the exact same configuration, package list, and build 
structure.

## Setup:
- Live system built with live-build using the following package 
selection:
live-boot
live-config
live-config-systemd
systemd-sysv
lightdm
lightdm-gtk-greeter
cinnamon-desktop-environment
network-manager
network-manager-gnome
xserver-xorg
xinit
calamares
calamares-settings-debian
task-german-desktop
task-german
locales

Content of /auto/config
#!/bin/sh

set -e

lb config noauto \
  --architecture amd64 i386 \
  --distribution trixie \
  --mirror-bootstrap http://ftp.at.debian.org/debian/ \
  --mirror-binary http://ftp.at.debian.org/debian/ \
  --bootappend-live "boot=live components locales=de_AT.UTF-8 
keyboard-layouts=de" \
  --debian-installer none \
  --interactive shell \
  --archive-areas "main contrib non-free non-free-firmware" \
        "${@}"


- No autologin is configured
- A user is correctly created by live-config (confirmed)
- LightDM is installed and enabled
- However, the system boots to a TTY login prompt instead of showing the 
graphical login

## Notes:
- On the **same hardware**, a Bookworm-based image with identical 
configuration **boots fine into LightDM** and starts the Cinnamon 
desktop correctly.
- On Trixie, LightDM fails to launch the graphical session.
- Nouveau fails to initialize properly on some modern NVIDIA GPUs (e.g. 
RTX 3080).
- This was not required in Bookworm for the same hardware.

## Additional note:
Installing `xinit` alone (without any manual `.xinitrc` configuration) 
allows the system to successfully start Cinnamon from the console via 
`startx`.

This confirms that X11 and the Cinnamon session are fully functional and 
properly installed. The graphical session only fails when starting via 
LightDM, which suggests a misconfiguration or missing default 
integration between LightDM and the Cinnamon session in the current live 
setup, I assume.

## Conclusion:
There appears to be a behavioral regression in the combination of 
live-config and/or live-build under Trixie:
- Either any of the DMs are not being configured properly during live 
system creation (tested lightdm, sddm)
- Or the greeter/session integration is incomplete?
- Or X11 startup fails silently on some hardware?
- Or the debian live build environment has to be used in a different way 
for trixie?

Btw. when installing Trixie with the RC1 Installer, there is no such 
problem as mentioned above, which leads me to the conclusion that 
something in the live-build-environment has changed, or is not working 
properly at the moment.

Please advise whether this change is intentional, and if not, whether 
Debian Live is expected to function out-of-the-box for graphical 
sessions under Trixie as it did under Bookworm.

Best regards,
Daniel Gestl