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I'm new to linux and this is my first installation of ubuntu 20.04 on ASUS ROG ZEPHYRUS G14 laptop. After installation, I can't change the screen brightness and my screen always show the highest screen brightness. After some time of changing grub in ubuntu forum, this is my attempts

  1. Add acpi_brightness=vendor or acpi_backlight=native or acpi_backlight=native or acpi_backlight=none to grub etc/default/grub still not working
  2. After that I installed brightness-controller-simple and brightness-controller and slide the brightness control to minimum and my screen brightness stays the same
  3. I installed xbacklight and run this command xbacklight -set 50 still didn't work

Note : I manged to install nvidia drivers on my laptop after using nouveau for 2 days and this is my result after run this command ls /sys/class/backlight/acpi_video0 >>> actual_brightness brightness max_brightness scale type bl_power device power subsystem uevent

My laptop specs : CPU : AMD Ryzen 7 4800HS GPU : NVIDIA GeForce GTX 1650 Ti 4GB GDDR6 RAM : 16 GB Kernel : Linux 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

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  • What happens if you run xrandr --output LVDS1 --brightness 0.5? (If it dulls your screen too much, reset it with xrandr --output LVDS1 --brightness 1. This isn't really a solution, I just want to see if it dims and we can go from there (maybe). If you're curious, each 0.1 is equal to 10% brightness, so 0.0 = 0% and 1 = 100%. LVDS1 is standard laptop display, but there's also DVI1 (and DVI2), HDMI1, DP1, and VGA1.
    – KGIII
    Jul 22, 2020 at 17:03
  • xrandr: Failed to get size of gamma for output default warning: output LVDS1 not found; ignoring xrandr: Need crtc to set gamma on. Jul 23, 2020 at 6:38
  • I got this error after run xrandr --output LVDS1 --brightness 1 or 0.5 xrandr: Failed to get size of gamma for output default warning: output LVDS1 not found; ignoring xrandr: Need crtc to set gamma on.
    – jittapont
    Jul 23, 2020 at 6:57

1 Answer 1

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I have the same laptop, same situation. Finally found the solution to be an upgrade to a new linux kernel.

Ubuntu 20.04 came with 5.4.x, Installing 5.7.15 fixed it for me. The hotkeys for brightness control still didn't work with fn but I mapped the f7 and f8 to that as I don't use them often.

Don't try to compile linux kernels yourself if you're not sure how that works, just use mainline. You might have to disable secureboot from the bios for some of the kernel versions. I had to disable it for 5.7.15

A comprehensive discussion for some other problems with this setup can be found at this reddit post

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  • I have the same laptop and upgrading linux kernel fixed the problem for me. Instruction for upgrading linux kernel can be found here: itsfoss.com/upgrade-linux-kernel-ubuntu, More over I install the brightness-controller. Sep 5, 2020 at 9:47

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