The ultimate reference seems to be in Arch Linux which is a site I've turned to many times to fix difficult problems.

Kernel Parameters

Looking at your cat /proc/cmdline there are no extra kernel parameters passed. The above link states:

Sometimes, ACPI does not work well due to different motherboard implementations and ACPI quirks. This includes some laptops with dual graphics (e.g. Nvidia/Radeon dedicated GPU with Intel/AMD integrated GPU). On Nvidia Optimus laptops, the kernel parameter nomodeset can interfere with the ability to adjust the backlight. Additionally, ACPI sometimes needs to register its own acpi_video0 backlight even if one already exists (such as intel_backlight), which can be done by adding one of the following kernel parameters:

acpi_backlight=video

acpi_backlight=vendor

acpi_backlight=native

If you find that changing the acpi_video0 backlight does not actually change the brightness, you may need to use acpi_backlight=none.

Try each of the acpi_backlight=xxxx options on your grub kernel paremeters line

When xbacklight doesn't work

You've tried xbacklight already and the link above addresses this:

On some systems, the brighness hotkeys on your keyboard correctly modify the values of the acpi interface in /sys/class/backlight/acpi_video0/actual_brightness (As we tried in comments) but the brightness of the screen is not changed. Brigthness applets from desktop environments (ie Ubuntu brightness setting slider bar) may also show changes to no effect.

If you have tested the recommended kernel parameters and only xbacklight works, then you may be facing an incompatibility between your BIOS and kernel driver.

In this case the only solution is to wait for a fix either from the BIOS or GPU driver manufacturer.

A workaround is to use the inotify kernel api to trigger xbacklight each time the value of /sys/class/backlight/acpi_video0/actual_brightness changes.

First install inotify-tools. Then create a script around inotify that will be launched upon each boot or through autostart.

Below is script you need to create called: /usr/local/bin/xbacklightmon

#!/bin/sh



path=/sys/class/backlight/acpi_video0



luminance() {

    read -r level < "$path"/actual_brightness

    factor=$((100 / max))

    printf '%dn' "$((level * factor))"

}



read -r max < "$path"/max_brightness



xbacklight -set "$(luminance)"



inotifywait -me modify --format '' "$path"/actual_brightness | while read; do

    xbacklight -set "$(luminance)"

done

There is a lot more in the link above but these steps are a good place to start.

Dedicated Forums

For additional support there are dedicated Linux Graphics forums:

• Phoronix Linux/AMD/Nvidia support with many Ubuntu users


• Nvidia Linux Developers Forum (with many Ubuntu specific topics)

Hi I apologise if this is something the clever people have already ruled out, as I am far from familiar with the command line, but after a reinstall i hit this problem and all the above solutions didn't work for me
(MSI pe706QE nvidia 960m).

I was editing /etc/default/grub by:

gksudo 'insert editor of choice not in quotes' /etc/default/grub

and noticed the nomodeset was still sitting in the bottom of the file (I don't remember permanently adding it) and removed it.

save the file and run:

sudo update-grub 

all working again with shortcut keys #noobie fail
hope this can help someone.

clone this repo and paste the script backlight.sh into /bin. then make it executable and after this open a root terminal and execute the following command.

sudo backlight.sh "brightness-level-number".

to clone the repository,

git clone https://github.com/el-beth/backlight.sh.git

You could install package of command xbacklight in terminal:

sudo apt-get install --reinstall xbacklight

After installation you could use command xbacklight as follows:

xbacklight -inc 20 # increase backlight by 20%

xbacklight -dec 30 # decrease by 30%

xbacklight -set 80 # set to 80% of max value

xbacklight -get # get the current level

Command xbacklight should work this way.

I have a Sony VPCEH notebook, I had the same problem.
I tried this solution that worked for me: http://ubuntuforums.org/showthread.php?t=2221452#6
Briefly:
With root privileges, create the file /usr/share/X11/xorg.conf.d/20-nvidia.conf with the following content

Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 410M"
Option "RegistryDwords" "EnableBrightnessControl=1"
EndSection

Log out and back in again to test.
And it gently adds: "If something goes wrong, simply delete that file and reboot to recover the system."
But I didn't need that addition. After logout and login the brightness control started to work again.
I hope it helps you too...

or this one after works with ubuntu 16.04 under my laptop sony VPCEJ2C5E but with nvidia 378.13 i don't have use for the moment the 390.25 drivers.

I was able to get my brightness keys working on my Lenovo W530 on Ubuntu 12.04.
These days X automatically configures itself, so creating an xorg.conf file might make your system inflexible. Instead you can add a section to a file in /usr/share/X11/xorg.conf.d/ and X will include that section in the configuration that it automatically generates.
So to get the screen brightness keys working with your Nvidia graphics card, create a file in the xorg.conf.d directory, e.g:
sudo gedit /usr/share/X11/xorg.conf.d/10-nvidia-brightness.conf
Paste the following into the file:

Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "Quadro K1000M"
Option "RegistryDwords" "EnableBrightnessControl=1"
EndSection

Log out and log back in, or reboot, and your brightness keys should now work!

enter image description here

Per wineunuuchs2unix's request, I am reposting my answer to a similar question here.

Try acpi_osi=

On upgrading to Bionic a few days ago, I encountered a similar problem (I have an NVIDIA GeForce GTX 1060 Mobile, but for me /sys/class/backlight is showing as empty).

In working through the backlight debugging procedure, I discovered a workaround via kernel parameters:

• In "Software & Updates" → "Additional Drivers", make sure that you have nvidia-driver-396 (or whichever metapackage is current; 396 is the latest at the time of writing) selected.


• Edit /etc/default/grub by running the command sudo nano /etc/default/grub (optionally replacing nano with your favorite editor).


• Find the line that sets GRUB_CMDLINE_LINUX_DEFAULT and add acpi_osi= at the end inside of the quotes. On most systems this will leave you with a line reading GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=".


• Save and exit the editor.


• Run the command sudo update-grub and reboot.

(If these steps do not work, restore your settings by repeating the process, but removing acpi_osi= when you edit the GRUB configuration.)

Another workaround, if it is an option for you, is to switch to a mainline kernel. In particular, I do not see the problem under mainline kernel version 4.17.

(Bug reported here.)

one program to solve all this problem !!!

i have GTX 1060 6Gb desktop ubuntu 16.04

NO need to do anything, just install brightness-controller with the ppa :

https://launchpad.net/~apandada1/+archive/ubuntu/brightness-controller/

solved the issue for me (see screenshots)
however it conflicts with redshift so you need to remove redshift

you can add it to startup for convenient use