[qubes-users] Fullscreen Multiple Monitors not possible?

Dear All,

In QubesOS R4.0, I have two monitors connected to form a large screen made up by two monitors side by side. I would like to achieve what does work in Debian, for example, that is a fullscreen window covering the entire screen (i. e., both monitors). This is particularly useful in rdp-seccions using freerdp. It can be achieved using:

xfreerdp /multimon

This leads to a freerdp connection across multiple monitors at leaset in Debian GNOME.

In QubesOS R4.0 it does work in principle. A window as wide as the set of monitors does get created. However, the fullscreen feature does not work. As soon as one clicks fullscreen, the window gets confined to one of the monitors. Of course, I did allow fullscreen as described here: https://www.qubes-os.org/doc/full-screen-mode/ And of corse, everything does work well with just one monitor connected. And yes, I do understand the security concept of normally not covering the entire screen but showng the window decorations including the VM color.

Is there a way to overcome that limitation? If “fullscreen” can be made to work across physical monitors in general, xfreerdp /multimon should work as well.

Thank you very much!

Michael Schefczyk

I guess that the xfreerdp just creates a window that is large enough and positioned in a way that hides the window borders. However, Qubes OS AFAIK does not allow the positioning for security reasons. However, you can do this yourself. It depends on your desktop environment and configuration, there is rough howto for Xfce:

  • Adjust the window position by alt+left-click and movement.
  • Adjust the window size by alt+right-click and movement.
  • If needed, make the window always-on-top by Alt+Space and selecting Always on Top.

I am pretty sure this can be automated by xdotool or something similar.

Vit Sestak ‘v6ak’

Thank you very much! The idea does make maximum sense, I think. However, without turning on full screen, there is the problem that the window - indeed created large enough to cover the full screen - will be truncated by the frame decorations. That brings issues particularly with the task bar. Once one clicks full screen, the screen gets limited to one monitor (-> “full monitor”). As far as I understand, one has the following instruments available in Qubes and freerdp:

  • allow_fullscreen and override_redirect_protection in guid.conf in dom0
  • the trapezoid slider “floatbar” created by xfreerdp /floatbar:sticky:off,show:always
    As far as I can tell, no combination of these instruments can resolve the issue. In Debian, the floatbar does allow maximizing the window across multiple monitors, but not in Qubes.

I nice solution might have been to accept the windows decoration and create the window slightly smaller (less height would be enough, because the top decoration is the main issue. That, however, does not seem to work because of freerdp: You need to set “xrfreerdp /multimon” but then you are unable to reduce the height. You can set a large screen, but without multimon, it does not extend accross monitors. This seems to be an endless cycle.

It would be good to know, if developers intend to change this behavior or not. I can accept the security concept of not welcoming fullscreen too much. However, when this is fully possible with one monitor but not possible with two monitors, that does not seem fully consistent - either or would make sense, but the number of monitors should not be the decisive factor from a concept standpoint.

I have forgotten to send the mail to qubes-users…

Well, in order to use the back from my first post, don’t use the actual fullscreen.

Vít Šesták ‘v6ak’