Xfce Forum

cleandesk

Member

Registered: 2025-03-31

Posts: 2

Display manager popping up unwanted, unable to set screen brightness

Hi all,

I have wiped out windows and installed debian 12 along with xfce as a first-time "real" personal computer. I got linux basics right but I'm nowhere near an advanced user.
I'm really happy with how I was able to setup my machine, especially with xfce and a little conky, it looks great, clean, it is practical and it runs smoothly on this low-spec machine.

However, there are a couple of things with the display and display settings manager that I can't quite figure out yet :

- Whenever I plug the charging cable in/out, the "display" window pops up.
-Also, on my keyboard, the "brightness up" and "brightness down" function keys are set on F11 and F12. But when I press them, the brightness won't change, although a status bar will pop up on screen with the brightness pictogram and move up or down according to the key pressed.
- Also when I press F11 or F12, the same "display" window pops up.

I'm guessing it has something to do with shortcuts and/or variables but I was unable to locate anything until now.

Any help appreciated !
T.Y.

(Computer is Lenovo 14w laptop)

Last edited by cleandesk (2025-03-31 12:54:32)

k3dAR

Member

From: Czech Republic

Registered: 2022-07-27

Posts: 112

Re: Display manager popping up unwanted, unable to set screen brightness

show display dialog after power cable (dis)connected is strange, maybe is detected as usb-c display port? :-)
you can try in xfce4-display-settings on tab Advanced set "When a display is connecter" set to "Do nothing"

about brightness, you can try some debug:
1. simple way, install brightnessctl package and try:

brightnessctl s 10%

if not work, try list all "light"(brightness,leds) device:

brightnessctl -l

and try self identify other device for screen and

brightnessctl -d other_device_name s 10%

2. not(?) simply lowlevel way: using sysfs, install file manager "mc" (midnight commander) for simplify
then run it with path to sysfs detected backlights devices as root

sudo mc /sys/class/backlight

you see one or more "directories", go to it and using F3 you can view actual_brightness and/or max_brightness, then set to specific value (here is not percent, but between 0 and max)

echo 100 > brightness

if one of this way work for you, then maybe fill bug report with info about your notebook, or can be reaaigned hotkey to use brightnessctl or some script using sysfs...

cleandesk

Member

Registered: 2025-03-31

Posts: 2

Re: Display manager popping up unwanted, unable to set screen brightness

Thanks for the help !

show display dialog after power cable (dis)connected is strange, maybe is detected as usb-c display port? :-)
you can try in xfce4-display-settings on tab Advanced set "When a display is connecter" set to "Do nothing"

I'm not seeing "when a display is connected" in Display > Advanced, all I got is "Configure new screens when they're plugged in", which is already toggled off.

about brightness, you can try some debug:
1. simple way, install brightnessctl package and try:

brightnessctl s 10%

if not work, try list all "light"(brightness,leds) device:

brightnessctl -l

and try self identify other device for screen and

brightnessctl -d other_device_name s 10%

I get multiple devices, including caps lock and num lock (which the keyboard doesn't have leds for)
acpi_video0
input0::scrolllock
input0::capslock
mmc1::
input0::numlock
mmmc0::

acpi_video0 seems to be the actual screen, but brightnessctl won't change the brightness for any of those devices, although it seems to execute the actual command and declares 'current brightness' as whatever value I just typed in.

2. not(?) simply lowlevel way: using sysfs, install file manager "mc" (midnight commander) for simplify
then run it with path to sysfs detected backlights devices as root

sudo mc /sys/class/backlight

you see one or more "directories", go to it and using F3 you can view actual_brightness and/or max_brightness, then set to specific value (here is not percent, but between 0 and max)

echo 100 > brightness

Was also unable to do it this way, I guess I'll be filing a bug report and get over it !

k3dAR

Member

From: Czech Republic

Registered: 2022-07-27

Posts: 112

Re: Display manager popping up unwanted, unable to set screen brightness

if doesn't work either via sysfs, then i'm almost sure (as sysfs is direct calling to linux kernel drivers), problem not be on Xfce side, but in linux kernel support for your HW, so maybe filling bug, but on kernel.org ?

anyway you can try add acpi_backlight kernel boot cmdline parameter:

1.editing Grub Bootloader control file,

sudo mcedit /etc/default/grub

# change
GRUB_CMDLINE_LINUX=""

# to
GRUB_CMDLINE_LINUX="acpi_backlight=vendor"
# save using F2 key, exit using two press ESC key

2. regenerate Grub configuration

sudo update-grub

3. reboot

If this not help, you can change acpi_backlight=vendor to acpi_backlight=video or acpi_backlight=native (and always, regegenrate grub config and reboot)

Last edited by k3dAR (2025-04-03 15:17:59)