How does GNOME Handle backlight, and how can I do it from CLI without root privileges?

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1

Good day, folks.
I recently purchased a new laptop from Tuxedo Computers of Germany, and all in all it is quite lovely.
I do have a question regarding backlight management, though. When in the GNOME desktop, there is a slider applet in the top bar that lets me adjust the brightness of the computer.
I am curious how GNOME accomplishes this without root privileges on a system with 8th gen Intel laptop processor and graphics. I want to do this myself in my i3wm configuration.
I have tried xbacklight, but it tells me that no displays have the backlight property. Currently I edit as super user the file “/sys/class/backlight/intel_backlight/brightness” and insert the appropriate value between 1 and ~3400.
If it is not feasible to adjust the backlight the way GNOME does it, I could really use any way to adjust it that does not require root permissions.
Thank you all so much!

2

Just a guess here, but probably using xrandr…

xrandr --verbose |egrep -i "brightness|gamma"

Try setting (eg HDMI-1) with something like

xrandr --output HDMI-1 --brightness 0.7
3

Yeah, I’ve used the brightness setting in Xrandr, and it works, but it does not affect the backlight, so it saves no battery.

4

Sorry, I’m not a Gnome user and didn’t realise that Gnome was adjusting backlight levels.

What (if anything) does the following report?

ls /sys/class/backlight
5

Right. That directory contains only the intel_backlight directory, which in turn contains


wilsontux@linux-idrr:~> ls -o /sys/class/backlight/intel_backlight/
total 0
-r--r--r-- 1 root 4096 Jul 18 18:53 actual_brightness
-rw-r--r-- 1 root 4096 Jul 18 18:53 bl_power
-rw-r--r-- 1 root 4096 Jul 18 18:53 brightness
lrwxrwxrwx 1 root    0 Jul 18 18:53 device -> ../../card0-eDP-1
-r--r--r-- 1 root 4096 Jul 18 18:53 max_brightness
drwxr-xr-x 2 root    0 Jul 18 18:53 power
lrwxrwxrwx 1 root    0 Jul 18 18:53 subsystem -> ../../../../../../../class/backlight
-r--r--r-- 1 root 4096 Jul 18 18:53 type
-rw-r--r-- 1 root 4096 Jul 18 18:53 uevent

I change my backlight by

sudo vim /sys/class/backlight/intel_backlight/brightness
6

Perhaps Gnome is using a D-Bus method…
https://wiki.archlinux.org/index.php/Backlight#Using_DBus_with_Gnome
Maybe the backlight can be adjusted in a similar fashion.

7

Okay, I gave that a try. The result in i3 is:

wilsontux@linux-idrr:~> gdbus call --session --dest org.gnome.SettingsDaemon.Power --object-path /org/gnome/SettingsDaemon/Power --method org.gnome.SettingsDaemon.Power.Screen.StepDown
Error: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SettingsDaemon.Power was not provided by any .service files

I’ll be right back with the results while GNOME is running.

8

Works fine in GNOME.

9

Now looking into other methods suggested on the Arch Wiki.

10

I got the package “illum” from the hardware experimental repository. Installed it, used systemctl to start illum.service, and now my backlight keys do exactly as intended. Thanks for linking me to that arch page!

11

I got the package “illum” from the hardware experimental repository. Installed it, used systemctl to start illum.service, and now my backlight keys do exactly as intended. Thanks for linking me to that arch page!

12

Good to read that you’ve found a method that works for you.