Ubuntu 20.04 brightness adjust not working

I am unable to adjust brightness levels through Gnome. I had the same issue with 18.04 but it was resolved there (honestly, I can't remember how).

lspci|grep VGA
00:02.0 VGA compatible controller: Intel Corporation Core Processor Integrated Graphics Controller (rev 18)

xrandr --output LVDS-1 --brightness 0.95
<-- this works through the terminal
excerpt from /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"

Thank you in advance.

The xrandr solution didn't worked for me. I have installed brighness-controller and worked well.

sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
sudo apt install brightness-controller

UPDATED: After I have upgraded to Ubuntu 21, this issue has fixed completely. My laptop buttons of brightness control works normally. No needed additional configuration.

I am having similar issue. There is no screen brightness slider on system menu (the one below the volume). I know that there is a workaround using xrandr that goes like this:

xrandr -q | grep " connected"

The output looks like:

DP-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
DP-3 connected primary 1920x1080+1920+0 (normal left inverted right x axis y axis) 477mm x 268mm

I am using a dual screen, so that is why I have 2 channels (DP-1 and DP-2). Then you can adjust the brightness by typing

xrandr --output DP-3 --brightness 0.8

Here, I am using 0.8 in monitor DP-3. Just do the same for the other monitor and we are all set.

However, I noticed that the screen brightness is oscillating and no solution that I found in the internet worked for me.

I had the same problem, which was solved following this post: How to Fix Brightness Keys Not Working in Ubuntu. The solution is quite simple:

Edit file /etc/default/grub, set

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor acpi_osi=linux"

Save the file and update grub:

> sudo update-grub

Restart the computer and it worked.

The rational behind the operations, as the author explained, is as follows:

ACPI is a power interface management standard which is implemented in operating system kernels. By default Linux kernel uses an inbuilt driver for keyboard keys, which is often non compatible with some keyboards.

Hence, we specify the option acpi_backlight=vendor which tells the kernel to take precedence of vendor driver over kernel driver. The option acpi_osi=linux tells the kernel to enable inbuilt ACPI workarounds for Linux drivers; which can be the case if the device driver has issues for Linux architecture.

In my case, I resolved this problem by upgrading the kernel version from 5.4 to 5.6.

$ sudo apt-cache search linux-image-5

Then it will return the list of available kernels. I installed linux-image-5.6.0-1028-oem which is listed at the bottom at the moment.

You can install it as follows.

sudo apt install linux-image-5.6.0-1028-oem

After reboot your system, you may see that your kernel is updated.

As a reference, my GRUB_CMDLINE_LINUX_DEFAULT is set to be that of the original one, i.e. GRUB_CMDLINE_LINUX_DEFAULT="quiet splash". In addition, I installed the brightness-controller but I'm not sure whether it helped me or not.

Hope this might help you.