Linux 6.1 Kernel Backlight question

Hi, I read this article on Ars Technica
TLDR: linux kernal 6.1 could break backlight control on old or “weird” laptops.

It sounds as if this will affect all linux varieties. But the blog post referenced only talks about redhat/fedora.

I went through the steps to determine if my laptop is affected and got stuck (I’m hardly proficient in linux) but I think my laptop would be affected. Does anyone know if this will in fact affect Manjaro down the line?

What did you get stuck with?

What he says to check is whether

ls /sys/class/backlight

returns only one result - and whether that is one of
“intel_backlight”, “nouveau_bl”, “amdgpu_bl0” or “radeon_bl0”

For me the result is:

ls /sys/class/backlight

this condition is met (and I could be affected)

Next is to add the


parameter to the grub command line and reboot with that change

You do this by editing /etc/default/grub
and add it to the line starting with:
and add that to what is already there, inside the quotes
(be careful - no typos, if at all possible :wink: )
followed by


and a reboot

Then do the check again.

I now have this result:

ls /sys/class/backlight
acpi_video0  acpi_video1  intel_backlight

I don’t know but it is more than likely IMO.

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Hi thanks for responding.
I got stuck here:
He says: if you don’t have an “acpi_video0” entry please first do “cat /proc/cmdline” and check that “acpi_backlight=video” is present there.

So I did this and it is not. I have no idea what this means–if I made a mistake appending to grub or if my laptop is affected. My grub was cut/paste appended, so no typos:
GRUB_CMDLINE_LINUX_DEFAULT=“quiet apparmor=1 security=apparmor udev.log_priority=3 acpi_backlight=video”

Any clarification or guidance you might have, I’d really appreciate!

It is kind of the other way around :wink: - at least as I understood it
What he said:

a second check is to boot with “acpi_backlight=video” added to the kernel commandline and then run “ls /sys/class/backlight” again, if you now additionally also have an “acpi_video0” entry then your laptop should work fine with 6.1, if you don’t have an “acpi_video0” entry please first do “cat /proc/cmdline” and check that “acpi_backlight=video” is present there.

cat /proc/cmdline

just verifies that you actually and successfully did the change

The result of that command should print the same as is in:
in /etc/default/grub

There is another way to add that acpi_backlight=video parameter
by editing the command line directly at boot time
This is not permanent, like the method that I described.
You just press “E” for edit at the grub screen …

Yes, so after I appended my grub, rebooted, and ran ls /sys/class/backlight again, I still have no “acpi_video0” entry. So then I did the cat /proc/cmdline, which also shows no “acpi_backlight=video” .

Also, all of the text outputs he asks for if you think you are affected returned nothing for me, except$ sudo acpidump -o acpidump.txt
sudo: acpidump: command not found

IMO that means that you are one of those people he needs to cooperate and send him the output of:

  • ls /sys/class/backlight > ls-backlight.txt

  • sudo dmesg > dmesg.txt

  • sudo dmidecode > dmidecode.txt

  • sudo acpidump -o acpidump.txt

send him these four text files

so that he can work on fixing it.

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Well thanks for your interpretation–I will send that to him, although there isnt much to go on.
Thanks again!

Those four commands produced no visible output, but four text files instead
(containing the output).


the acpidump command, which did not work, is available when you install the package:
from the repos

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Ah, thank you! I’ve located those and will send them. I hope he can find an a solution, I’d hate to have to give up my old laptop!

I really appreciate your time ans patience!


don’t forget to install acpica so that you can also include the probably pretty important acpidump data

I’m downloading it now, thanks!

Hi, just to make sure: you don’t write that you actually updated grub, as @Nachlese wrote, after appending to its GRUB_CMDLINE_LINUX_DEFAULT= configuration. If you don’t run the grub update, /proc/cmdline will not change.

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I thought that was weird - but then I still forgot and missed it

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Ha its only weird if you know what youre doing…
I totally did not update grub I just rebooted.
I will try again…Thanks!!!

I didnt update grub. Crap, thanks!

Well that was the crux. I updated grub and now it shows the magic
ls /sys/class/backlight
acpi_video0 intel_backlight
So it looks like I get to keep using my old laptop.

Thank you both so much!

dont forget to revert back to original kernel parameters. if you keep acpi_backlight=video in your kernel parameters, backlight controls may not function anymore

it has nothing to do with manjaro, anyone using kernel 6.1 on any distro will be subject to it

Updates from Hans: