Comment 5 for bug 1892973

Some additional information:

When the boot sequence is
- GRUB boot to recovery mode
- Drop to root prompt
- Remove a driver and install a driver
- Exit root prompt (Ctrl-D)
- Resume normal boot as per the recovery mode menu

Then the display comes up at a degraded resolution (1024x768) but no gnome-session hang occurs in response to some of the reliable triggers (typically, attempting to launch Firefox, Google Chrome, or navigate gnome-settings).

Booting normally (via restart or hard-reset) brings up the display at maximum resolution and gnome-session hangs immediately on one of the reliable triggers.

I noted this previously.

To test whether resolution is the issue, I booted normally. gnome-settings hangs gnome-session, so instead, I ran
```xrandr -s 1024x768```
which was immediately effective. I then accessed gnome-settings and it triggered another gnome-session hang.

The conclusion is that degraded screen resolution itself does not prevent gnome-session hangs.

Reviewing /var/log/syslog and the systemd journal, as well as /var/log/Xorg.0.log reveals that gdm3 recognizes the monitor by manufacturer and model and correctly picks up its configuration capabilities when the system boots normally. This does not occur, however, when one boots first to recovery mode, changes drivers, and resumes normal boot.

To test whether a recovery mode session alone prevented a gnome-session hang, I then booted to recovery mode, did NOT change drivers, then resumed normal boot. Interestingly, the display came up in high resolution notwithstanding the prior xrandr reconfiguration. /var/log/Xorg.0.log reflected that gdm3 did identify the monitor. And, most importantly, the reliable triggers immediately caused a gnome-session hang.

The conclusion, then, is that a recovery mode session alone does not prevent a gnome-session hang. One must change the driver during that recovery mode session, to prevent it (albeit at the cost of degraded screen resolution).

To test whether simply removing and installing the same driver during a recovery mode session would be sufficient to avoid a gnome-session hang, I experimented with that. On resuming normal boot, the screen came up at full resolution and the usual triggers produced a gnome-session hang.

The conclusion, then, is that a change of drivers is necessary during a recovery mode session to prevent a gnome-session hang after resuming normal boot from recovery mode. Again, this is at the cost of degraded screen resolution, and the protection will not persist through a normal boot.