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My laptop is a DELL 3521 with dual graphic cards, which usually cause some problems, and I have switched off the AMD Radeon card.

Now, when I want to turn the brightness down by dragging the brightness bar in the "Brightness and lock settings" and I close the window, nothing changes, and when I open "Brightness and Lock Settings" again, the brightness bar turn back to its previous state!

So, is it something is the system or I did some kind of mistake?

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Try it once.. It has solved all problems about brightness! Including mine!!

  • Open terminal ( Ctrl+Alt+T ) and type:

    sudo gedit /etc/default/grub

    You will find this line in the new opened window: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

  • Change it to:

    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
  • Save and close the window and type this in the terminal:

    sudo update-grub
  • Restart your system..

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