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

Thomas Goirand thomas at goirand.fr
Sun Mar 29 22:18:20 UTC 2015

Hi Yves-Alexis,

I have experienced the same issue as described by Fabien.

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). 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 

Increasing the brightness on the lightdm password prompt doesn't work. 
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.

Before I knew this trick, I thought my laptop was crashed. So I just 
powered off, then on again. But then when lightdm gets back, it sets the 
brightness to zero again (meaning screen is off in my case), and I can 
see nothing. The only way is again, to type my login and password 
blanking (without any control to see if I typed correctly), then when X 
start, I can set the brightness again.

I can confirm that the issue is in lightdm, because gdm doesn't have 
this issue. I'm also using systemd. I'm using the Nouveau driver (and 
probably also the intel i915 since my laptop has 2 cards). I'm not sure 
this is related to video board and driver, but I thought it was a good info.

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...

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.


Thomas Goirand (zigo)

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