>That particular display behaviour, of turning off the display after 10
>minutes and turning on again on mouse move, is most likely a display
>management feature in Xorg, and something you can tune with the "xset"
>command.

>Firstly, you can use "xset q" (in a terminal) to see the Xorg display
>settings.

>You may turn off its "Screen Saver" and "DPMS" with "xset -dpms s off"

>See "man xset" for details.

Just been playing around with this and found the following:
xset s off # sets the screensaver timeout to zero but this changes nothing.
xset -dpms # instantly kills the session and throws you back to the
login screen.
xset dpms 0 0 0 # sets all the dpms timers to zero, eliminates the
session being killed.

dpms seems to have a potentially lethal effect on the xsession,
depending on its parameters. Disabling it entirely instantly kills the
session. Setting the timers for standby, suspend and off to some large
value minimise the impact, setting the to zero removes the impact
completely, I imagine the different timers may differ in their
effects, so maybe only one of them needs to be set to zero.

Checking my other machines (all daedalus) they all have different dpms
parameters not knowingly set by me.
A clean daedalus install has standby/suspend/off set to 600, 0, 900
My personal laptop has 7200, 7200, 14400

TLDR:
xset dpms 0 0 0 s off stops the problematic behaviour, but making this
change permanent presumably means editing files somewhere in /etc/X11

Thanks to you all for your continued help.

Bob

On Fri, 7 Nov 2025 at 12:42, Ralph Ronnquist <rrq@???> wrote:
>
> On Fri, Nov 07, 2025 at 08:58:50AM -0300, sawbona@??? wrote:
> > Hello:
> >
> > On 7 Nov 2025 at 10:36, Bob Bowles wrote:
> >
> > > ... 10-minute mark the screen went blank. Then I moved the
> > > mouse, and the screen came back, just like a screensaver, Except I
> > > don't have a screensaver ...
> > Interesting indeed.
> >
> > Like I may have mentioned I run Devuan Daedalus with the XFCE desktop
> > and SLiM, this with two NVidia cards running three monitors using the
> > nouveau drivers for a 3840x1024 desktop.
> >
> > The layout is as follows: the left monitor is the primary one,
> > sharing the first Nvidia card with the right monitor, the centre
> > monitor running off the second card.
> >
> > Even though I made sure that there were no XFCE (or other) power
> > management applicatios running, after some time (never timed it) the
> > left and right monitors will go off, just like yours ie: screen saver
> > mode.
> >
> > Moving the mouse brings them back on, the difference being that I do
> > not get logged off.
>
> That particular display behaviour, of turning off the display after 10
> minutes and turning on again on mouse move, is most likely a display
> management feature in Xorg, and something you can tune with the "xset"
> command.
>
> Firstly, you can use "xset q" (in a terminal) to see the Xorg display
> settings.
>
> You may turn off its "Screen Saver" and "DPMS" with "xset -dpms s off"
>
> See "man xset" for details.
>
> Ralph.
>
> >
> > It is rather annoying because those two monitors are old (but
> > perfectly working) 19" Samsing SyncMaster 940n which use FL lamps.
> >
> > FL lamps are affected by coldish room temperatures in wintertime and
> > as a result the screen is dimmed while thay warm up, particulalry if
> > they have over 34K hours on them like these. 8^°
> >
> > I never bothered to research further on how to turn this 'feature'
> > off as I expect the FL lamps will last a bit longer by keeping it as
> > it is.
> >
> > SLiM seems to be off the hook and maybe XFCE too as this happens even
> > without my being logged in.
> >
> > ie: bringing my system up and going to make my morning espresso while
> > it boots. If enough time has passed, on coming back to my desk I will
> > need to move the mouse to get the log-in screen on the primary
> > monitor.
> >
> > Note that the centre monitor does *not* get put to sleep.
> >
> > It would seem (?) that you may be experiencing the same thing in your
> > setup.
> >
> > Best,
> >
> > A.
> >
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--
Dr RJ Bowles

25 Wellesley Avenue North Norwich NR1 4NT
+44 (0)7912 297662

Skype: bob.john.bowles
Email: bobjohnbowles@???