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I switched from Ubuntu 20.04 to Ubuntu 24.04 recently. The output of uname -r -v is 6.8.0-36-lowlatency #36.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Jun 13 17:00:08 UTC 2024. Everything seems to be working well except for setting the screen brightness level. At first, the keyboard shortcuts (Fn+F6 and Fn+F7) did nothing, and I was able to get them to work by using the following modification of the GRUB file:

# GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
# GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor acpi_osi=linux"
# GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force acpi_backlight=native"
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force acpi_backlight=video"

(Note that the commented lines correspond to the initial setting, followed by two unsuccessful tries which were suggested on different forums.)

At this point, the keyboard shortcuts "work" in the sense that I get the feedback from the system indicating that my actions are doing something, as shown in the following screenshot: screenshot of screen brightness adjustment feedback Unfortunately, this does not translate into an actual change of my screen's brightness.

I have a Dell G15 laptop, in case this matters.

Attempts at using xbacklight yield the message "No outputs have backlight property", so I tried commands from the this post but I am uncertain if should and how to modify my /etc/X11/xorg.conf file:

sudo find /sys/ -type f -iname '*brightness*' yields:

/sys/kernel/debug/dri/0000:00:02.0/i915_params/invert_brightness
/sys/devices/platform/alienware-wmi/leds/alienware::global_brightness/brightness
/sys/devices/platform/alienware-wmi/leds/alienware::global_brightness/max_brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::numlock/brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::numlock/max_brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::capslock/brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::capslock/max_brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::scrolllock/brightness
/sys/devices/platform/i8042/serio0/input/input2/input2::scrolllock/max_brightness
/sys/devices/platform/dell-laptop/leds/dell::kbd_backlight/brightness
/sys/devices/platform/dell-laptop/leds/dell::kbd_backlight/brightness_hw_changed
/sys/devices/platform/dell-laptop/leds/dell::kbd_backlight/max_brightness
/sys/devices/pci0000:00/0000:00:14.3/leds/phy0-led/brightness
/sys/devices/pci0000:00/0000:00:14.3/leds/phy0-led/max_brightness
/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/actual_brightness
/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness
/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/max_brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-2::lan/brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-2::lan/max_brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-1::lan/brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-1::lan/max_brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-0::lan/brightness
/sys/devices/pci0000:00/0000:00:1d.5/0000:04:00.0/net/enp4s0/enp4s0-0::lan/max_brightness
/sys/devices/virtual/sound/ctl-led/speaker/brightness
/sys/devices/virtual/sound/ctl-led/mic/brightness
/sys/module/video/parameters/hw_changes_brightness
/sys/module/video/parameters/brightness_switch_enabled
/sys/module/xe/parameters/invert_brightness
/sys/module/i915/parameters/invert_brightness

ls -alrt /sys/class/backlight points to:

lrwxrwxrwx  1 root root 0 Jul  5 12:50 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0

The files in /sys/class/backlight/acpi_video0 and /sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0 are linked, and the values in the files actual_brightness and brightness now appear to be modified (in both directories and both files) by the expected keyboard shortcuts. That said, there is still no change in actual screen brightness: whether the values are changed manually or using the shortcuts, this does not impact the screen's brightness, despite what appears to work in this answer.

Finally, this other current post which has some traction appears to be dependent on the specific laptop model, which is not the same as mine. This question deals with a potentially similar issue on the same laptop as mine, but has no answer.

plywood98
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1 Answers1

-1

This has been solved in a somewhat unsatisfactory way, as I am not sure exactly at what point in my process of messing around things actually started to work out. I am posting this answer as a "best guess", in case anyone else encounters this.

  • My laptop is a Dell G15 5511 running Ubuntu Studio 24.04.
  • I installed the nvidia drivers by using the command sudo apt install nvidia-driver-470 nvidia-dkms-470.
  • Be careful: if you attempt to install version 535, which is the latest version at the time of writing this, then I recommend having a backup to revert to just in case... For some reason, version 535 did not work for me, and I was unable to successfully uninstall 535, so I was lucky to be able to roll back my system using timeshift to a time before the installation of the driver in order to install version 470 from scratch.
  • I commented all the custom GRUB_CMDLINE_LINUX_DEFAULT settings in the GRUB file (leaving only GRUB_CMDLINE_LINUX="").

After this, the shortcut keys worked and acted on the actual brightness of the screen.

plywood98
  • 1