I have a System76 Lemur Pro. Since upgrading to F37 I’ve lost the ability to control the screen brightness in Gnome and via the function keys. The folder /sys/class/backlight doesn’t exist and from what I’ve been reading it should be there.
$ lspci -k | grep -EA3 'VGA|3D|Display'
00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02)
DeviceName: VGA compatible controller
Subsystem: CLEVO/KAPOK Computer Device 1401
Kernel driver in use: i915
Kernel modules: i915
Kernel includes "acpi_backlight=intel
$ cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt2)/vmlinuz-6.1.5-200.fc37.x86_64 root=UUID=28730e9c-57a9-4dd4-9aa7-f4eb451cae1f ro resume=/dev/mapper/fedora_localhost--live-swap rd.lvm.lv=fedora_localhost-live/root rd.luks.uuid=luks-7a875e5b-a21e-4e99-9cf6-399a7bd21e5a rd.lvm.lv=fedora_localhost-live/swap rhgb quiet splash acpi_backlight=intel
$ lsmod | grep i915
i915 3436544 53
drm_buddy 20480 1 i915
drm_display_helper 208896 1 i915
cec 81920 2 drm_display_helper,i915
video 65536 1 i915
ttm 94208 1 i915
Attempting to use the function keys to adjust the brightness yields the following in the syslog:
Failed to set new screen percentage: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._gsd_5fpower_5fmanager_5ferror.Code1: No usable backlight could be found!
What other info can I provide to help fix this?
On the next boot try removing this
splash acpi_backlight=intel from the kernel command line and see what the result is. I do not have and have never had that in my kernel command line and I see this on my laptop. My laptop has intel + nvidia GPUs.
$ ls /sys/class/backlight/intel_backlight/
actual_brightness bl_power brightness device max_brightness power scale subsystem type uevent
Removing those entries didn’t work.
Aha! I set it to “acpi_backlight=native” and it worked! In case someone else finds this thread…
edit /etc/default/grub and include “acpi_backlight=native” at the end of your GRUB_CMDLINE_LINUX_DEFAULT stanza:
Save your config and run “sudo grub2-mkconfig”. Reboot.
ref: Backlight - ArchWiki
ironically, I often find the best documentation for Fedora in the Archlinux wiki.
Sorry to pile on what looks like the solution to this question, but one clarifying question that I was having trouble getting a clear answer on through Google - is
sudo grub2-mkconfig the full command there, or is there a path that you had to type afterward, like
sudo grub2-mkconfig --output=<filename here>?
I’m no grub expert, but all I typed was what is in the quotes.
The actual command must have an output file for it to write to a file. Without specifying an output file it writes the output to the screen.
The command is
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
To find out what a command does use the man page, as
You also can peruse the many threads that contain that command, or see the official documentation at
Thanks for the file location info!
FWIW, that page on the Fedora Docs site has a banner at the top that it is deprecated, and “large parts of it are no longer current”, so I was a bit hesitant to assume.
I appreciate the help!
That doc page was updated fairly recently and I believe is current for all releases since fedora 34.