[Pkg-xfce-devel] Bug#773913: Bug#773913: Lightdm switches immediately to a black screen

Yves-Alexis Perez corsac at debian.org
Thu Apr 9 10:01:19 UTC 2015

On jeu., 2015-04-09 at 09:55 +0200, Thomas Goirand wrote:
> On Mon, Mar 30, 2015 at 12:18:20AM +0200, Thomas Goirand wrote:
>  >> What happens is, if I leave my laptop unused for a (very) long
>  >> period
>  >> of time idle, it goes into darkness (slowly fades out, then full
>  >> screen black).
>  >
>  > So something in your desktop environment handles the brightness and
>  > sets it to minimum?
> Yes, the screen saver.

That's not enough information. Also note that brightness is not DPMS.
>  >> When I want to wake-up my latop, I just press any key. This wakes up
>  >> the laptop, but it does *not* set the screen brightness back to
>  >> normal.
>  >>
>  >> Increasing the brightness on the lightdm password prompt doesn't
>  >> work.
>  >
>  > I assume your laptop needs something in userspace to handle the
>  > brightness keys, then?
> I believe my mate desktop is somehow handling this.

I have no idea about what MATE does, this is purely random guesses here.
You might want to investigate more.
>  >> However, if I just type my password (blankly, hoping it works...),
>  >> then I get to X (using the mate Desktop in my case), then brightness
>  >> control works, and I can see the screen again.
>  >
>  >Because MATE handles the brightness keys.
> Yes, and lightdm should as well.

I don't think that's the job of a login manager, actually (my opinion is
that it was the kernel job, but they disagree). I've forwarded upstream,
it's their call anyway.
>  >> I believe that the best way to fix it, is to make sure that the
>  >> brightness controls are *always* working in lightdm. If I get back to
>  >> lightdm with a black screen, I don't really mind if I can fix that by
>  >> increasing the brightness...
>  >
>  > Sure, but I'm not sure handling the brightness keys are really the
>  > role of a login screen. I'll forward this upstream but don't hold your
>  > breath.
> If we can't handle the brightness keys, then just setting-up the 
> brightness could be a quick and dirty fix-up. Here's a few way to do it 
> on my laptop:
> # This needs root:
> echo 4792 > /sys/class/backlight/intel_backlight/brightness
> # This needs xbacklight to be installed, but this is from userland:
> xbacklight -inc 100%

And you're back to handling manually everything, adding support for
specific graphics cards and what not. Definitely not the role of a login
> Do you know if the above can be set somewhere in the lightdm config as a 
> hook script or something? If that is for *me* only, this type of hack is 
> enough (but of course, a more generic / less dirty way to fix things for 
> everyone else would be better...).

See /etc/lightdm/lightdm.conf (you can edit it, or put overrides
in /etc/xdg/lightdm/lightdm.conf.d, remember to correctly set the
section), for example:

# display-setup-script = Script to run when starting a greeter session
(runs as root)                                                   


# greeter-setup-script = Script to run when starting a greeter (runs as

>  >> If I may help to debug the issue in any way, let me know. I'd be
>  >> happy to do whatever you propose to debug the issue or test some
>  >> fixes.
>  >
>  >It might help to know which kind of laptop it is.
> My laptop is a Lenovo T440p. I have attached the output of dmidecode and 
> lspci, if that helps.

So yes, that's a Windows 8 laptop which needs userspace handling for
brightness keys.

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