LMDE 6 → LMDE 7 Upgrade Fails to Start Cinnamon Desktop on NVIDIA Systems (RTX 4070)

The upgrade path from LMDE 6 to LMDE 7 consistently results in a TTY1 Lockout on systems using modern NVIDIA proprietary drivers (series 550). The primary issue is a failure of the default Display Manager, LightDM, to initialize the graphical session after the kernel and drivers are installed.

System Information

Initial OS: Linux Mint Debian Edition 6 (LMDE 6)

Target OS: Linux Mint Debian Edition 7 (LMDE 7 'Gigi')

GPU: NVIDIA GeForce RTX 4070

Driver Version Used: nvidia-driver-550.163.01-2 (automatically installed during upgrade)

Steps Taken / Observed Failure

Ran mintupgrade from LMDE 6 to LMDE 7.

NVIDIA driver 550.x.x was installed and DKMS modules were built (confirmed via dkms status).

Upon reboot, the system failed to launch the graphical environment and consistently dropped to tty1 (text login) despite driver installation success.

Critical Workaround/Solution

The system was stabilized only after replacing the default display manager:

Logged into tty1.

Installed the alternative display manager: sudo apt install gdm3

Set GDM3 as the default when prompted.

Executed sudo reboot.

Conclusion: GDM3 successfully manages the NVIDIA driver initialization and starts the Cinnamon session on LMDE 7 where LightDM fails. This strongly suggests a compatibility or configuration error within the LightDM package or its interaction with the new Xorg configuration under LMDE 7.

Request

Please investigate the LightDM/NVIDIA configuration files during the upgrade path to prevent this TTY lockout for other NVIDIA users.

Start by reproducing the LMDE 6 to LMDE 7 upgrade with an RTX 4070 and NVIDIA driver 550, then inspect the LightDM configuration and the mintupgrade path after the system falls to tty1. Compare the failed LightDM startup with the working GDM3 setup. Done means the upgraded system starts the Cinnamon session through LightDM without requiring a display-manager replacement.