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Debian 12 install - monitors won't turn off

Hi, all. Finally migrated from Kubuntu to Debian 12 over the weekend. It’s working great, as I figured it would, with one exception: The system isn’t turning the monitors off after 10 minutes. It’s blanking them, but they’re clearly still on.

One monitor is on an AMD graphics card, the other is on the motherboard Intel adapter.

Debian 12 with KDE Plasma running on Wayland with sddm login. It previously worked fine on Kubuntu (which I believe was running X11). It’s a fresh Debian install on a different drive; I didn’t overwrite the Kubuntu installation.

In the Energy Saving settings, I have “Screen energy saving” checked with a delay of 10 minutes. (I have “suspend session” turned off - one, because I don’t want the computer to sleep or suspend, and two, because when I woke it up again, the graphics were garbled and I had to reboot.) As I said, it does blank the screens, but they’re still clearly on. I want them to go into power save mode.

I’ve tried running dpkg-reconfigure and selecting sddm, no change. In KDE’s background services, I tried turning off KScreen 2, but that didn’t help (though I’m not sure if I rebooted after turning it off, now that I think about it).

I found advice somewhere that suggested deleting .config/powermanagementprofilesrc and rebooting; I did that, no change.

I did notice yesterday that the monitors had shut off…after a very long time of being idle. I’m not sure how long, but more than overnight, for certain.

Any advice or suggestions? Unfortunately, searching is difficult, because I get a lot of results where the screen blanks when it shouldn’t. I haven’t found much for this problem.

I used the same installer on my laptop to do the same migration (also with KDE Plasma and sddm) and it works fine there.

Frederic ,

I have MX (Debian based), I had kind of the same problem, my DELL monitor didn’t sleep. To fix it, I had to go in the monitor settings and set the input mode to “HDMI1” instead of Auto. It looks like the auto mode was maybe sending message or something that prevented it from sleeping.

limelight79 OP ,

Interesting, but I haven’t changed that either.

And, gah, it just worked normally. WTF. I haven’t changed anything yet this morning.

9488fcea02a9 ,

I’ve had this problem for years. I contributed to one of the existing bug reports for kscreen on this.

If i dont login to kde (sddm login screen), the screens will shut off normally… But once i login, the problem starts. So i concluded the problem is with kscreen2. I even tested by killijg kscreen2 and the problem goes away

bugs.kde.org/show_bug.cgi?id=413618

limelight79 OP ,

Interesting. I’ll try the kscreen2 kill again.

9488fcea02a9 ,

Sorry, i dont have all the links available, but the root cause of the problem is apparently with the amdgpu driver

Kscreen was supposed to implement some kind of workaround, but i lost track of how that was going.

limelight79 OP ,

Thanks. That gives me something to look into. Wonder why it didn’t happen under Kubuntu…I kept it up to date, but it still might have been too old in some way (X11 instead of Wayland or something).

9488fcea02a9 ,

Most likely x11 vs wayland

limelight79 OP ,

I’m starting to think this really is it, because it again worked while I was away eating lunch - it turned off my monitor that is hooked to the Intel integrated video. The other monitor is currently switched to my work laptop.

bloodfart ,

Switch to x11 and use xscreensaver will fix that problem.

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