Brightness problem on Ubuntu 20.04 (System panel works, but nothing change)

Question

I just installed ubuntu 20.04. Backlight control works through the brightness applet and works via hotkeys, but nothing change, the display brightness remains the same. Here's what I've done:

Modified and updated GRUB file on /etc/default/grub from GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor". This did not work.
Create a file (20-intel.conf) on /usr/share/X11/xorg.conf.d with this lines:
Section "Device" Identifier "card0" Driver "intel" Option "Backlight" "intel_backlight" BusID "PCI:0:2:0" EndSection This did not work.
Create a file (80-backlight.conf) on /usr/share/X11/xorg.conf.d with this lines:
Section "Device" Identifier "Intel Graphics" Driver "intel" Option "AccelMethod" "sna" Option "Backlight" "intel_backlight" BusID "PCI:0:2:0" EndSection This did not work.

Then, I noticed my sys/class/backlight folder has two folders inside, one named acer-wmi and another one named intel_backlight both of them have the files mentioned here such as bl_power brightness actual_brightness max_brightness type. If I change the brightness level using both the applet and hotkeys, the actual_brightness file on acer folder changes (between 0 to 15), but not any file on intel's folder change. Of course, the display brightness remains the same.

After change the grub again with this kernel parameter acpi_osi=Linux the hotkeys do change the displays brightness, but I still cannot adjust the brightness using the slider, if I do that, the slider works (moves), but nothing changes.

I notice that now on my sys/class/backlight folder, the acer folder mentioned changed its name for acpi_video0 while Intel's folder remains the same. When I make changes on brightness using the hotkeys, the files on both folders now reflects the changes, but if I use the slider provided by Ubuntu, nothing happen to the display but files on acer's folder change. Just the acer files, not Intel's one. Curious. It's seems like Ubuntu is modifying files but in the incorrect folder.

I've had the same. Try this https://askubuntu.com/questions/1230937/ubuntu-20-04-brightness-adjust-not-working — Giorgos Saridakis, May 27 '20 at 23:12
Does this answer your question? Ubuntu 20.04 brightness adjust not working or Brightness problem Ubuntu 18.04 LTS — Nmath, May 28 '20 at 04:40
you should post your last update as an answer and mark it as the accepted answer,as an extra bonus you will get some reputation. — trond hansen, May 28 '20 at 05:42

score 3 · Answer 1 · answered May 28 '20 at 12:11

I found the solution for my problem. If you find that changing the acpi_video0 backlight does not actually change the brightness, you may need to use the kernel parameter acpi_backlight=none. I did it and now both the slider and hotkey works and there is only one folder on sys/class/backlight, the Intel's one. Because there is nothing else, the system and the keys are forced to use that one. I also noticed that my brightness can be more or less brighter since Intel's parameters are higher than the 0 to 15 ones on acpi_video0.

kindly elaborate how should i change mine – Atif Shafi Nov 25 '21 at 17:05 — Atif Shafi, Nov 25 '21 at 17:05

Brightness problem on Ubuntu 20.04 (System panel works, but nothing change)

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