Xscreensaver causing my monitors to turn off and on repeatedly when its power management features are active; how to fix?

Question

Something weird is up with my Xscreensaver 5.15 configuration on Debian Wheezy. I have two Dell U2412M monitors hooked up to a single graphics card (one over native DVI and one over HDMI output to DVI input).

When I disable power management through the Xscreensaver configuration tool, by unchecking "Power Management Enabled" in the Advanced tab, then everything works fine, except of course I don't get any power management on the monitors. I'm running Xfce 4.8 and in its Power Manager have set "Put display to sleep" and "Switch off display" to Never in both the "On AC" and "On Battery" settings categories.

Here is what xset q has to say about DPMS with the above-mentioned settings:

DPMS (Energy Star):
  Standby: 900    Suspend: 0    Off: 0
  DPMS is Disabled

My keyboard is hooked up through the USB hub built into one of the monitors, and the mouse is hooked up through the USB hub built into the other. Both monitors are connected directly to the computer with no intervening USB hub.

If I change Xscreensaver's power management settings to the following:

• Power Management Enabled: yes
• Standby After: 15 minutes
• Suspend After: 0 minutes
• Off After: 0 minutes
• Quick Power-off in Blank Only Mode: no

then sure enough the monitors do enter power savings mode in accordance with those timeouts, as expected. However, something is causing the monitors to then start turning fully off, and back on, repeatedly. Aside from the regularly flickering light being rather annoying and this obviously nullifying any power savings, it also fills up my system logs with keyboard disconnection and reconnection log entries from the USB subsystem:

May 10 02:20:13 yeono acpid: input device has been disconnected, fd 9
May 10 02:20:17 yeono kernel: [24226.670088] input: Unicomp Inc G+SpaceSaver as /devices/pci0000:00/0000:00:12.2/usb1/1-1/1-1.2/1-1.2:1.0/input/input52
May 10 02:20:47 yeono acpid: input device has been disconnected, fd 9
May 10 02:20:47 yeono kernel: [24257.280219] hub 1-1:1.0: hub_port_status failed (err = -71)
May 10 02:20:50 yeono kernel: [24260.457788] input: Unicomp Inc G+SpaceSaver as /devices/pci0000:00/0000:00:12.2/usb1/1-1/1-1.2/1-1.2:1.0/input/input53
May 10 02:21:04 yeono acpid: input device has been disconnected, fd 9
May 10 02:21:07 yeono kernel: [24277.355231] input: Unicomp Inc G+SpaceSaver as /devices/pci0000:00/0000:00:12.2/usb1/1-1/1-1.2/1-1.2:1.0/input/input54

I probably made some change when this started, but I'm at a loss as to what that change might have been. Old logs don't reveal anything useful; the most recent upgrade I did before this apparently started was related to MySQL. The only remotely relevant and reasonably close in time I can find is an upgrade of xdg-utils from 1.1.0~rc1+git20111210-6+deb7u1 to 1.1.0~rc1+git20111210-6+deb7u2 about a week before when these problems seem to have started.

I have been able through a process of elimination to narrow down the issue to turning off and on Xscreensaver's power management features. If Xscreensaver's DPMS is off, all is well; if it's on, I get this weird behavior.

What do I need to do to get power management back to working normally?

Answer 1

Conveniently X has multiple ways of enabling a screen saver and xset is probably the oldest and easiest way of manipulating what is going on. It has been superseded by newer technologies but it should still work fine.

The biggest downside of xset is that it is not very smart and doesn't plug-into newer frameworks very well. For instance, newer frameworks may be smart enough to not wake up the monitor when an input device is plugged in.

In regards to the problem you are having however, I'd suggest blacklisting the USB device, one possible tutorial on doing this is given below (assuming that you don't need whatever that device is providing).

http://projectgus.com/2014/09/blacklisting-a-single-usb-device-from-linux/