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This seems to be a hardware issue rather than a Ubuntu issue, but nevertheless, here goes. I have an Acer ao756-2617 with Ubuntu 14.04, elementary os luna, bodhi linux, and zorin os 8. most of these if not all are Ubuntu or Debian related (not sure bout Bodhi). anyway, every time i try to use my brightness controls for the screen, they don't work. when i use them, all i get is the animation on the upper right corner that its working, but it doesn't actually do anything. so i did some research. I found that I could manually change the brightness using one of two things:

  1. sudo intel_backlight <% no. of brightness>

  2. echo <no. from 0 - 976> | sudo tee - /sys/class/backlight/intel_backlight/brightness

Apparently, the file controlling the brightness for the screen is the one described on the command above. I did an acpi_listen to see what I got when I used the Fn+brightness controls and I got:

video/brightnessdown BRTDN 00000087 00000000
video/brightnessup BRTUP 00000086 00000000

(those come from Ubuntu 14.04. the other OS's give similar output)

This suggests that these keys are being mapped to be handled to acpi drivers, instead of the intel ones. I tried changing that, but I have no idea what to do. I dont even know if I'm on the right track. granted, I know that a backlight problem mustn't be much of a concern for the devs, but this could help others like me. help, anyone?

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2 Answers 2

I got a fix for my Dell 5521 laptop, which works for Ubuntu 14.04 but it will work for kernels v3.13+

  1. Open /etc/default/grub

    sudo nano /etc/default/grub
    
  2. Change line

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
    

    to

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"
    
  3. Then save Ctrl+O, exit Ctrl+X and run:

    sudo update-grub
    
  4. Reboot

Explanation is that acpi adds its own backlight control even if one is already present which is intel_backlight, adding this line forces acpi to use the Intel backlight.

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I've got the same problem with my lenovo v570, but I figured out thas there is a problem with the kernel or with the modprobe. The brightness buttons change in my opinion the brightness from /sys/class/backlight/acpi1_video/brightness this is a wrong file. Since I had install the kernel 3.7.6, this Problem was gone. Try to install another kernel lower then 3.8.x (This was the last working kernel for me)

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