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I am not 100% that it is related to the ->18.04 update, could be some other update. Nevertheless, it was a coincidence in time with the release update, so I think it might be it.

In short, this functionality: https://help.ubuntu.com/stable/ubuntu-help/display-brightness.html.en

is no longer working. I can move the slider, but brightness doesn't change. The keyboard shortcut works: it moves the slider, but the brightness doesn't change. As a temporary solution I installed and use xbacklight, but it would be nice to be able to again control brightness with dedicated hotkeys. Any advices? If nothing works, I will bind some other keys to xbacklights....

Maciek
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  • Do you have dual NVIDIA and INTEL graphics cards? If so, try purging the proprietary NVIDIA drivers and installing the nouveau driver (Open Source NVIDIA driver). This might be the cause. – Raffa Mar 19 '20 at 09:36
  • I never knew it, checked only now. I have nvidia GK107GLM [Quadro K1100M] with the proprietary driver nvidia-driver-390. The specs does not say anything about it being dual. – Maciek Mar 19 '20 at 09:41
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    Probably the installed driver is not compatible with the updated kernel. You could refer to this answer for info and try in the terminal first this sudo apt purge nvidia-* then this sudo ubuntu-drivers autoinstall then reboot after that. – Raffa Mar 19 '20 at 09:46
  • Also asked via https://ubuntuforums.org/showthread.php?t=2438852 – guiverc Mar 19 '20 at 09:50
  • I never even knew about dual cards, but now as I read about it, it seems that my CPU specification says about "Intel HD Graphics 4600", so maybe this laptop has two graphics processing units indeed. – Maciek Mar 19 '20 at 09:51
  • @Raffa, I will try the solution you suggest (indeed it seems quite probable that this is exactly what happened), but after the coronavirus quarantine is over: I currently need my laptop to work remotely and can't risk screwing the drivers! ;-) Will post an update here if it worked. Thanks a lot for your suggestion. – Maciek Mar 19 '20 at 09:53

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Thanks to @Raffa for the solution. It did not work out of the box, i.e. when I applied it, it did not change anything, because it reinstalled the driver in the nvidia-driver-390 version. Raffa was nevertheless right about the source of the problem and this is what I did to fix it:

I first added the following PPA: How do I install the Nvidia drivers?

Then, I applied a fix to this bug: https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-390/+bug/1768050 and finally after:

sudo apt purge nvidia-* && sudo ubuntu-drivers autoinstall

I had a new version of the driver, i.e. nvidia-driver-415 installed, which works smoothly with my 4.15.0-101-generic kernel. Thanks!

Maciek
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