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I followed this guide to install bumblebee on my Dell XPS 15 9560 running Ubuntu 17.04 in an attempt to fix the fan-always-on problem. This fixed issue with the fan and the power draw, but now I can't adjust the screen brightness.

When I followed the guide my screen was set to minimum brightness, and now it is stuck that way. The brightness function keys bring up and adjust the brightness bar icon and appear to be working, but the screen brightness does not adjust.

When I boot the screen starts out bright, but then during the boot sequence it dims and stays that way. If I boot into Windows 10 I can adjust the brightness normally.

Changing acpi_backlight=none to acpi_backlight=vendor on the GRUB_CMDLINE_LINUX_DEFAULT line in /etc/default/grub, running update-grub and rebooting has no effect. If I change the entire line from the one suggested in the linked bumblebee install guide to the one suggested in this answer then my system does not boot at all.

Imran
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2 Answers2

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May not be a universal solution, but try this:

sudo tee /sys/class/backlight/acpi_video0/brightness < /sys/class/backlight/acpi_video0/max_brightness

If you are using the Intel graphics card rather than the Nvidia one:

sudo tee /sys/class/backlight/intel_backlight/brightness < /sys/class/backlight/intel_backlight/max_brightness

Alternately, try replacing N with various small numbers (1 - 7 work for me but that is probably hardware specific) in the following:

sudo echo N | sudo tee /sys/class/backlight/acpi_video0/brightness
Ocramius
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Lew Rockwell Fan
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    I don't have an acpi_video0 directory, but I have intel_backlight and dell_backlight directories. brightness and max_brightness in dell_backlight both contain 15 and brightness and max_brightness in intel_backlight are 75 and 1500 respectively. Using my brightness function keys changes the value in dell_backlight/brightness but does not affect the actual screen brightness, but setting intel_backlight/brightness to 1500 worked! – Imran May 24 '17 at 16:57
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    Good. Sharp of you to poke around and figure out how to adapt that. And good of you to post the details. It will help somebody else. – Lew Rockwell Fan May 24 '17 at 17:05
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I tried adding acpi_backlight=none to the GRUB_CMDLINE_LINUX_DEFAULT string in /etc/default/grub, running sudo update-grub2 and rebooting one more time and this solved my problem. The brightness keys now correctly control my screen brightness. I don't know why this didn't work on the first try.

Imran
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