Arch Linux

berberus

Member

Registered: 2023-11-01

Posts: 4

[SOLVED] No backlight controller found, /sys/class/backlight is empty

Hello, i just installed arch linux with i3wm.
Everything works pretty well for now, except this thing i've been working on the entire day and i can't find the solution !
I am trying to adjust my monitor backlight (i am on desktop, not laptop) using a simple shortcut.
I have a nvidia RTX 2070 super gpu, and i am using nouveau drivers, (i don't know if that helps)

I tried to use this tool :https://gitlab.com/cameronnemo/brillo and also this one : https://man.archlinux.org/man/light.1.en
And both give me the following error : "No backlight controller was found"

I searched a bit and i found that i don't have anything in my /sys/class/backlight directory. And if i am not wrong, that means that the kernel is not detecting any backlight device.

Now i don't really know what to do, i did some reasearch and tried different things but nothing worked..

So i am asking for your help please if someone can explain me how this works i would like to understand why i don't have any backlight controller detected, and how can i fix that.

Last edited by berberus (2023-11-02 13:51:40)

Khere

Member

From: Italy

Registered: 2020-03-04

Posts: 170

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Is you user added to group video for the light package?
If no add it to the group and then reboot.
If this doesn't work either, try to use ddcutil https://man.archlinux.org/man/extra/ddc … cutil.1.en

---

Fan of Giorgio Moroder & Mohammad Ammax enemy

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 23,300

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Your desktop monitor does not expose a backlight on any system, so all of this is normal. You can use and must use, the linked ddcutil utility assuming your monitor implements support for that protcocol. As far as the wiki goes, the section you must follow is: https://wiki.archlinux.org/title/Backli … l_monitors

Last edited by V1del (2023-11-02 09:12:02)

berberus

Member

Registered: 2023-11-01

Posts: 4

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Your desktop monitor does not expose a backlight on any system, so all of this is normal. You can use and must use, the linked ddcutil utility assuming your monitor implements support for that protcocol. As far as the wiki goes, the section you must follow is: https://wiki.archlinux.org/title/Backli … l_monitors

Hey ! Thanks for your help. So here is what i did : I loaded the i2c-dev kernel module, added my user to i2c group, i can now detect all active i2c devices.
i installed ddcutil, and tried the different commands to adjust brightness, and that works.
But i still have the same problem, the backlight utilities (brillo, light, brightnessctl etc) all seem to be needing files in /sys/class/backlight ; but i still don't have any, the wiki says "Alternatively, one may use ddcci-driver-linux-dkmsAUR to expose external monitors in sysfs. Then, after loading the ddcci kernel module, one can use any backlight utility."  but after installing ddcci-driver-linux-dkms, i still have an empty /sys/class/backlight directory. And so i can't use  the backlight utilites.

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 23,300

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Did you load the module/reboot since doing so?

berberus

Member

Registered: 2023-11-01

Posts: 4

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Did you load the module/reboot since doing so?

Yes, i did : make then make load if that's what you mean.

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 23,300

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Not quite, you'd load the kernel module with e.g.

modprobe ddcci_backlight

and if you want that autoloaded you'd create e.g. a  /etc/modules-load.d/ddcci_backlight.conf with

ddcci_backlight

Last edited by V1del (2023-11-02 11:22:58)

berberus

Member

Registered: 2023-11-01

Posts: 4

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Not quite, you'd load the kernel module with e.g.

modprobe ddcci_backlight

and if you want that autoloaded you'd create e.g. a  /etc/modules-load.d/ddcci_backlight.conf with

ddcci_backlight

Thank you so much !!! Yeah, that wasn't quite right, indeed x) Now it works ! And, most importantly, I understand how it works and why it didn't work initially. My next mission will be to lower the brightness below the lowest level allowed by my monitor ! Anyway, thank you very much for your help!

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 23,300

Re: [SOLVED] No backlight controller found, /sys/class/backlight is empty

Glad to hear, please mark as [SOLVED] by editing the title in your first post, so that others know that there might be a solution to be found.