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I have just upgraded from 18.04.5 LTS to 20.04.1 LTS and appear to have lost the ability to blank the screen/monitor despite it working fine previously. I am using the 'Ubuntu' desktop environment and Settings > Power > Blank Screen is set to 1 minute. Despite no mouse/keyboard activity the display is however not turning off after this time (indeed I tried leaving it all night but to no avail). The feature works fine if I select 'Unity' for my desktop environment on login.

Does anyone know what might be wrong or how I might go about debugging the issue?

MJNewton
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    Same here. I just switched from gdm3 to lightdm under 20.04.03LTS, and now the screen never turns blank even though it should according to the Power Saving setting. I confirm this is still a bug. – Norbert S Nov 23 '21 at 18:05

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I really went round the houses with this, including messing around with xset dpms which seemed to work... for a while at least. I couldn't get the settings reported by xset -q to persist between sessions and even when set within a session something kept overwriting them.

What I did in the end was stumble across someone talking about display managers. I confirmed mine to be lightdm bit I'd also heard about gdm3 (the default for Ubuntu 20.03?). So, I ran dpkg-reconfigure gdm3 and set it to be the default and, after a reboot, found that the power settings in Settings were taking effect!

So, I've solved my problem but arguably haven't fixed it as such. Good enough for me and hopefully might be of use to someone else should they stumbled across this same issues.

MJNewton
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