Debugging GNOME screensaver/screen blanking

I have an issue with the GNOME screensaver, or to be more precise with the “screen blank” power-saving option. When not using the machine, after the configured timeout, the screens go blank and the monitors go to standby. However, about 2 seconds later GNOME decides to switch on the screens again. The screens then stay on for several seconds - and then briefly switch off again. And this endlessly repeats. Super annoying, since the screens keep flashing.

It’s not related to the monitors (I have three different ones connected/tested) - affects all of them. It’s also not related to any input device (keyboard/mouse). It also happens when no input devices are connected.

I’m looking for a log file which could explain why the gdm screen saver keeps waking up immediately after switching off the screens. I haven’t found any log messages yet, which would explain the behaviour.

Which log file specifically should I look into? And/or are there any debug switches to provide more verbose output about why the screen saver keeps waking up?

@thorstenbr Your running an AMD gpu I suspect, if so add the kernel boot option amdgpu.dc=0.

It’s an older machine using a Nvidia GTX660 with the nouveau driver.

So far, I assumed this to be related to GDM incorrectly detecting some kind of input - and therefore waking up. The delay between switching the screens on and off feels like the delay when you are moving the mouse - but then not making any input (entering the password to unlock). So it quickly goes back to screen power-save mode again (just to almost immediately wake up again). So I was hoping for some kind of log explaining which input exactly triggered GDM to show the lock screen again.

@thorstenbr ahh ok, then it should show in the output from journalctl. Perhaps open a terminal and then just tail the log journalctl -f and see if you can pick up what is happening.

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FWIW, I see similar behavior on my tumbleweed system with an Nvidia 3090ti and the proprietary drivers.

For me, the screens blank for a couple of seconds, then come on for a couple seconds, and then turn off and stay off - usually. Sometimes they come back on and never turn off again. It’s very inconsistent.

I’ve tried to dig into this a couple of times, but also have not found any logging anywhere that would explain this behavior.

@hendersj not see that here with my T400, but it was an issue with my RX550 ( HDMI connected monitors fail to sleep and instead turn back on when amdgpu.dc=1 (#662) · Issues · drm / amd · GitLab).

It looks similar, but also looks to be specific to AMD GPUs, unfortunately. I’m trying to remember, but I think at one point, I was using a DP cable on one of the monitors, but the monitor I was using that on has a Chromecast plugged into it, so when the GPU on my PC would tell it to sleep, the input would change, so I never knew if that was actually showing the same issue.