I have now determined that it seems specific to my turning off the 
monitor. If I leave it on even overnight, X keeps working as expected. 
The problem is that the monitor is not turned off - so the backlight is 
going on a black screen all the time.

James Pulver
CLASSE Computer Group
Cornell University

On 09/12/2016 09:27 AM, James M. Pulver wrote:
> Cross posted from serverfault:
>
> I'm having the weirdest issue. We use SL7.2 and have a network home
> directory and AD + SSSD for auth. This means I can go to different
> computers and get a consistent home dir as well as UID/GID etc. I have a
> physical KVM to set up computers more easily.
>
> I started having an issue where my workstation would stop displaying X
> to my monitor. The monitor will say "No Signal" It would work fine until
> I switched away via the KVM to another computer, when I switched back X
> would not display. I could connect via Bomgar and see my X session, it
> was fine. I could ctrl-alt-F3 and the virtual terminal would display,
> but the only way to get X back was to reboot.
>
> I thought it might be the KVM, so I connected the monitor via DVI
> directly to the workstation. No change.
>
> I thought it was an issue with the hardware or the OS install, so I set
> up a brand new Lenovo P510 with a new SL7.2 install. Now it will loose X
> if I just don't use it for a while (I think it's the screen locking?).
>
> I thought it might be the monitor - maybe it's old and loosing signal,
> or the new Display port to DVI adapter can be funky, so I installed a
> brand new BENQ GW2765, connected directly via Display Port to the nVidia
> card (this card only has Display Port connectors - 4x). No change.
>
> However, this last time Bomgar could not show the X session...
>
> So now I'm thinking - it HAS to be software, and it has to be something
> in my configuration. But I don't really even know where to start looking
> - /var/log/messages and /var/log/Xorg.0.log don't show anything that's
> obvious to me.
>
> How can I fix X not coming back?
>