Ubuntu – Cannot change backlight brightness Ubuntu 14.04

14.04backlightbrightnessintel graphics

This morning I found that I cannot change the brightness of my Dell XPs 13 laptop's display anymore. I tried the following to change the brightness

  • Use keyboard brightness keys
  • Run the commands shown below
  • Boot with kernel option acpi_backlight=vendor. This resulted in a dell_something folder being present in the /sys/class/backlight folder. Changing the brightness file in that folder does not help.
  • Add 'intel_backlight' to xorg.conf
  • Set "load legacy option ROM" BIOS option to enabled and "secure boot" to disabled
  • Boot with kernel option i915.disable-pch_pwm=0
  • Boot from a fresh Ubuntu 12.04 USB stick installation. I can still not control the brightness. This is strange as the laptop came preinstalled with 12.04. Maybe this a hardware problem?
  • Install latest intel video driver

Any ideas why this broke suddendly? I've upgraded from 12.04 to 14.04 in April and till yesterday the brightness keys were working fine.


echo 100 > /sys/class/backlight/intel_backlight/brightness
echo 100 > /sys/class/backlight/acpi_video0/brightness

Best Answer

I got a fix for my dell 5521 laptop, working for Ubuntu 14.04 but will work for kernels v3.13+.

  1. Open /etc/default/grub

    sudo nano /etc/default/grub
  2. to change the line



    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"
  3. then save and exit and

  4. run

    sudo update-grub
  5. then reboot

The explanation is that ACPI adds its own back light control even if one is already present which is intel_backlight, adding this line forces CPI to use the Intel back light.

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