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

Thomas Goirand thomas at goirand.fr
Thu Apr 9 21:13:45 UTC 2015

On 04/09/2015 12:01 PM, Yves-Alexis Perez wrote:
> 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.

I'm not sure how to collect the information that you need then.

> Also note that brightness is not DPMS.

I'm well aware of it, and my screen isn't off using DPMS, it seems that 
my laptop just turns the LCD completely off when brightness is set to 
zero, as much as I can see.

>>   >> 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.

Well... I don't really care who's job it is, if at least it is possible 
to set the brightness whenever I need to type my password. You agree 
that this is a needed functionality, right?

>>   >> 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
> manager.
>> 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)
> or:
> # greeter-setup-script = Script to run when starting a greeter (runs as
> root)

Thanks for the tips! I'll try.

>>   >> 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.


Thanks for your helpful replies so far.


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