Here is what it looks like when I go to the "change brightness" option. I am booting in recovery mode because when I boot to normal Ubuntu mode there is nothing you can see on the screen, I can only hear the login sound.

So I thought I would need to change the brightness but neither Fn + F6 works, nor do I get an option to change the brightness in the settings.


  • Perhaps my answer here may be a useful workaround. As for the normal mode, I'd suggest you install different greeter - like lightdm-gtk-greeter Mar 10, 2015 at 14:43
  • got this after enter this in terminal bash: /sys/class/backlight/acpi_video0/brightness /sys/class/backlight/acpi_video0/brightness: No such file or directory Mar 10, 2015 at 14:48
  • what does this say: ls /sys/class/backlight/ Mar 10, 2015 at 14:50
  • it does nothing when i enter ls /sys/class/backlight/ Mar 10, 2015 at 15:09
  • Did you verify that your <kbd>Fn</kbd>+... keys work? That they weren't hijacked or shadowed? Mar 10, 2015 at 15:36

1 Answer 1


Manual way

Works for some systems, though not yours, apparently, since ls /sys/class/backlight/ shows nothing for you. Sometimes instead of intel_backlight you'll have acpi_video0, or something else.

You can manually change the brighntess level all the way down (to disable it altogether) by doing echo 23 > /sys/class/backlight/intel_backlight/brightness as a root. "23" is the desired brightness level. If you put "0", the screen will look blank.

From Adam Ryczkowski's comment here, which helped my friend in similar case.

Empty /sys/class/backlight/ means unrecognized hardware

When I noticed your exchange with @Serg, I thought "why would that folder be empty" and search showed this:

If /sys/class/backlight/ is empty, that means that the kernel thinks you have a big bad old CRT attached to the system and that you have to turn the big fat knobs named "Brightness" and "Contrast" on the from to change... well, brightness and contrast...

source: @Fabby's answer to another AskUbuntu question.

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