Qemu + KVM here has began failing to start due to internal error some snapshot before then 16 June: sudo journalctl -u libvirtd.service | grep 'internal error: Cannot' giu 14 08:19:21 AsusN752Host libvirtd[7440]: internal error: Cannot find start time for pid 4704 giu 14 08:19:21 AsusN752Host libvirtd[7440]: internal error: Cannot find start time for pid 4837 giu 15 09:00:12 AsusN752Host libvirtd[32607]: internal error: Cannot find start time for pid 32207 giu 15 22:50:10 AsusN752Host libvirtd[29695]: internal error: Cannot find start time for pid 29616 giu 16 08:33:32 AsusN752Host libvirtd[8810]: internal error: Cannot find start time for pid 5842 giu 16 08:33:32 AsusN752Host libvirtd[8810]: internal error: Cannot find start time for pid 8740 giu 16 22:27:09 AsusN752Host libvirtd[10612]: internal error: Cannot find start time for pid 10430 giu 19 08:25:22 AsusN752Host libvirtd[8045]: internal error: Cannot find start time for pid 7775 Since then, the solution has been to restart the LibVirtD after the KDE Desktop has finished to load. The VirtManager can then connect to qemu://System again. Hope this help.