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Pranav
Asked: 2019-04-23 21:12:27 +0800 CST

Both brightness bar and button is not responding. (Ubuntu 19.04)

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So I followed this post but I am stuck because of this output:

ln: failed to create symbolic link '/sys/class/brightness': Operation not permitted.

What I wanted to try is:

$ cd /sys/class This directory should contain a soft link called brightness to the brightness device discovered in the previous step. Should it be missing, create it: $ sudo ln -s /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness /sys/class/brightness

Note that: There is no "brightness" folder inside /sys/class. But there is "backlight" folder. What should I do? Should "brightness" folder/file?

Creating the file, gives me, "Operation not permitted". I used "cat > brightness" command. It didn't work. Now the only option I have is to create a folder.

Meanwhile, I can't control the brightness through the "brightness" button. Even moving the "Brightness bar" manually doesn't respond.

Screenshot of Brightness bar

Brightness button & bar used to work, but dunno what happened. How do I resolve this issue?

brightness 19.04

2 Answers

  1. Try this:

    sudo -s
mount -o rw,remount,suid -t sysfs sysfs /sys
ln -s /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness /sys/class/brightness

    That should fix it.

    Actually, you don't even need to do that. All those steps are not required if you want to control brightness. You already have the brightness control, all this command is doing is creating a small link to that.

    Do this: 

    #For finding out current brightness:         
cat /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness

#To set brightness to a level        
echo 100 > /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness

    Change the number to whatever you like. There is an upper limit. This is not usually a percentage. So you should be able to set brightness to 281, for example.

    Your last error was using cat command incorrectly. cat command show the content of a file.

    • 1
  2. Best Answer

    For some reason, changing this line solved the issue:

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"

    For that, do this: 

    $cd /etc/default
$sudo gedit grub

    Put above line and restart. This didn't work before but it worked somehow. Try using "video" instead of "vendor" which is very unusual. But it might help.

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