Reading this appears to be useful https://github.com/LibVNC/x11vnc/issues/102 In short, having no monitor connected together with vsync appears to be the issue here. So you should try to disable vsync and/or compositing of your desktop. Also in short: https://github.com/LibVNC/x11vnc/commit/97d632c1c02e5e2e5e65882228f02978080c5e52