CentOS - Dec 2017 - Switch off laptop screen when docked with lid close - CentOS 7

Hi,

I'm using CentOS on a laptop that part of the time is connected to a 
docking station with two monitor connected to it. When the laptop lid is 
docked, its lid is closed, as the system is placed in a position where 
it's not convenient to keep it open, let alone look at the screen.

Now in the past, with CentOS 5 (on a different laptop, but same physical 
config) and 6, the screen has automatically been switched off in this 
configuration - it's been as if it was no longer there after I docked 
the machine, which is of course exactly what I want. After I recently 
switched to CentOS 7, however, I no longer get this behaviour. Even 
thought I can't see the screen, it's obvious that it's on, or at
least
the system thinks so - it appears in display config, and? xrandr 
mentions it as "connected".

Any idea what's going on? Shouldn't the screen just switch of 
automatically? What part of the system is supposed to handle this 
anyway? And what's the best way around my problem? I've already disabled
the screen in Display preferences, of course, but it seems like the 
situation should ideally be handled at a more global level, and also, 
*my* display config obviously has no effect on the login manager. Which 
means I can't really log in while the machine is locked, as the monitor 
is then still on, and guess where the login window appears...

Thanks,

- Toralf

On 05/12/17 08:53, Toralf Lund wrote:
> Hi,
> 
> I'm using CentOS on a laptop that part of the time is connected to a
> docking station with two monitor connected to it. When the laptop lid is
> docked, its lid is closed, as the system is placed in a position where
> it's not convenient to keep it open, let alone look at the screen.
> 
> Now in the past, with CentOS 5 (on a different laptop, but same physical
> config) and 6, the screen has automatically been switched off in this
> configuration - it's been as if it was no longer there after I docked
> the machine, which is of course exactly what I want. After I recently
> switched to CentOS 7, however, I no longer get this behaviour. Even
> thought I can't see the screen, it's obvious that it's on, or
at least
> the system thinks so - it appears in display config, and? xrandr
> mentions it as "connected".
> 
> Any idea what's going on? Shouldn't the screen just switch of
> automatically? What part of the system is supposed to handle this
> anyway? And what's the best way around my problem? I've already
disabled
> the screen in Display preferences, of course, but it seems like the
> situation should ideally be handled at a more global level, and also,
> *my* display config obviously has no effect on the login manager. Which
> means I can't really log in while the machine is locked, as the monitor
> is then still on, and guess where the login window appears...
> 
> Thanks,
> 
> - Toralf
> 
Running CentOS 7/Gnome 3 and I also use two external monitors connected
to my docking station. When laptop is docked (so lid is closed) internal
display is turned off and only external displays are used.
Same in gnome settings/displays : it shows my "Built-in display" as
'lid
closed' and so only my external 24" displays as enabled (as Primary and
Secondary) (and I confirm that display is also off, and only gets back
to enabled when I undock and open the  lid)

-- 
Fabian Arrotin
The CentOS Project | https://www.centos.org
gpg key: 56BEC54E | twitter: @arrfab

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On 05/12/17 14:16, Fabian Arrotin wrote:
> On 05/12/17 08:53, Toralf Lund wrote:
>> Hi,
>>
>> I'm using CentOS on a laptop that part of the time is connected to
a
>> docking station with two monitor connected to it. When the laptop lid
is
>> docked, its lid is closed, as the system is placed in a position where
>> it's not convenient to keep it open, let alone look at the screen.
>>
>> Now in the past, with CentOS 5 (on a different laptop, but same
physical
>> config) and 6, the screen has automatically been switched off in this
>> configuration - it's been as if it was no longer there after I
docked
>> the machine, which is of course exactly what I want. After I recently
>> switched to CentOS 7, however, I no longer get this behaviour. Even
>> thought I can't see the screen, it's obvious that it's on,
or at least
>> the system thinks so - it appears in display config, and? xrandr
>> mentions it as "connected".
>>
>> Any idea what's going on? Shouldn't the screen just switch of
>> automatically? What part of the system is supposed to handle this
>> anyway? And what's the best way around my problem? I've already
disabled
>> the screen in Display preferences, of course, but it seems like the
>> situation should ideally be handled at a more global level, and also,
>> *my* display config obviously has no effect on the login manager. Which
>> means I can't really log in while the machine is locked, as the
monitor
>> is then still on, and guess where the login window appears...
>>
>> Thanks,
>>
>> - Toralf
>>
> Running CentOS 7/Gnome 3 and I also use two external monitors connected
> to my docking station.
Thanks. That's useful information.
>   When laptop is docked (so lid is closed) internal
> display is turned off and only external displays are used.
Just wondering, what's the normal sequence of operations when you 
connect? In my case it's generally,

 1. Close the lid of the laptop (when carrying from somewhere else.0
 2. [ The laptop is suspended via the close action ]
 3. Connect to the dock
 4. Hit the power button so as to return from suspend.
> Same in gnome settings/displays : it shows my "Built-in display"
as 'lid
> closed' and so only my external 24" displays as enabled (as
Primary and
> Secondary) (and I confirm that display is also off, and only gets back
> to enabled when I undock and open the  lid)
Anyhow, I think I've found what the issue is, at least in part: I 
actually switched to the LightDM display manager, on a somewhat 
experimental basis. I had GDM at first, but never actually docked the 
laptop before the chance. I didn't really think about that when I posted 
the original message, and also thought the laptop lid etc. would be 
handled at a different level, but it would appear not. If I use GDM 
(which I've now tested once more), the display is disabled at the login 
screen, and this "translates" into the desktop, at least if its
"local"
monitor config is cleared. With LightDM, all 3 screens are active, the 
the setting is also carried through to the desktop.

I've tested this with MATE as well as GNOME.

This means I have a solution of sorts, but I'd really like to know why 
the LightDM has this problem, and the details of how these things work 
are still rather blurry...

- Toralf



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