When using RealVNC Viewer as a client to connect to KDE Desktop Sharing(krfb-4.8.5-2.4.1.x86_64) things work as expected. However, if a screen saver has been set(blank screen in this case), the VNC session does not properly reset or disengage the screen saver. The VNC session lights up the screen, but the screen goes dark/blank again within seconds resulting in a slow and extremely annoying flashing of the VNC session. The VNC session is unusable like this. If the screen saver is disengaged by activity at the actual server console then the VNC session becomes stable, as it should be. I have tried disabling the screen saver, via the KDE configuration, while this blinking is occurring, but the blinking continues. If the screen saver is disabled prior to it blanking the screen, as when it is disabled at the console, the VNC session behaves properly. However, the VNC session should work properly regardless of screen savers. Exactly as described in Bug 283773 Reproducible: Always Steps to Reproduce: 1. Use RealVNC Viewer to connect to a krfb session where the blank screen saver is running. Actual Results: Screen saver clears and screen lights up on both ends. Screen on both end goes black/blank after a few seconds. Expected Results: Screen saver should have gone away and VNC session should have worked normally. Screen saver should not have returned until after 4 minutes of inactivity. krfb-4.8.5-2.4.1.x86_64
See also the following: Bug 134765 This problem appears to have been showing up since 2006!
I can confirm this with krfb from KDE 4.5.5 on FreeBSD and multiple VNC clients including krdc, Chicken of the Sea, and Apple's Desktop Sharing. Also, this seems to be a duplicate of 134765, 147091, and 283773 which are all related to the screen saver reactivating too soon.
Further fighting with this issue has caused me to discover that it is connected with Xorg's Display Power Management Signalling(dpms). Setting dpms off mitigates the issue. If I issue the following command within a terminal within the VNC session, the screen blanking issue is eliminated until dpms is turned back on: xset dpms force off Permanently disabling dpms and thus the ability for the monitor to sleep is not reasonable. Therefore, I have to turn dpms back on with the following command when I leave the VNC session: xset dpms force on
*** This bug has been marked as a duplicate of bug 134765 ***