On 2022-04-04 5:17 a.m., davidson wrote:
On Sun, 3 Apr 2022 Juan R.D. Silva wrote:
Hi folks,
Debian 11 on Dell M4800 Mobile Workstation with Nvidia Quadro K2100M
card.
I've been using the system with full (100%) screen brightness for
rather long time. Today I wanted to reduce it and to my astonishment
found that GNOME "progressed" to the point when even this basic
feature has gone.
The function keys work, the sliders move. Everything is dandy, except
it has no effect on the actual brightness, which stack at 100%. Even
setting the brightness in BIOS to 50% instead of 100% has no effect.
Google revealed a lot of complaints but so far I've not found any
really helpful suggestion. Worse, I even couldn't find any trace of
this being a bug of some sort.
Anyone can help here? I'm getting old and my eyes sore. :-(
I'll show you what I do. I don't use GNOME, but maybe it will work.
Four steps:
1. Confirm this directory has expected contents:
$ ls -p /sys/class/backlight/acpi_video0/
actual_brightness bl_power brightness device max_brightness
power/ subsystem type uevent
It has "brightness" and "max_brightness" files. So far so good.
2. Find out what counts as maximum brightness. (I think I have seen
this vary from laptop to laptop):
$ cat /sys/class/backlight/acpi_video0/max_brightness
7
3. Find out what value current brightness is:
$ cat /sys/class/backlight/acpi_video0/brightness
5
4. As root, write some value less-than-or-equal-to maximum brightness
(found in step 2) into "brightness" file. For example, when 5 is too
bright, I might try replacing that with 4.
# echo -n 4 > /sys/class/backlight/acpi_video0/brightness
That is all.
Hope this helps.
Sorry for the rant but it looks that either GNOME folks decided they
know it best what it should be for everyone or they are so busy with
frequent "nice" GUI changes and re-designs that there is no time
left for actual functionality. Fake controls and sliders doing
nothing?.. This is really climax.
I have no patience for figuring out where graphical desktops hide (or
document) their "user friendly" configuration tools, so I can
sympathise.
Something like the above procedure (maybe with some extra exploration
of /sys/class) has always worked for me.
Good luck. Hope this helps.
Looks that I failed to deliver the point in my post.
All 4 steps are correct. And I most certainly can happily change the
value in the /sys/class/backlight/acpi_video0/brightness file to
whatever I want. The problem is it does not have any effect on the
actual/physical screen brightness.
The change of the value in the
/sys/class/backlight/acpi_video0/brightness only results in the slider
in Brightness settings and other related GUI controls being carefully
and precisely re-positioned to reflect the new value in
/sys/class/backlight/acpi_video0/brightness.
This is why there was a rant. Looks that like in GNOME moving the
sliders around is the only goal. Well, that's been achieved. Greetings
to the devs. :-) Sorry for another one. :-)
Thanks.
