Description of problem: I'm pretty sure this is a libvirt bug, although it might be a qemu thing. But killing the user libvirtd process fixes it, so that seems to indicate libvirt. Launching libguestfs gives: libguestfs: error: could not create appliance through libvirt: internal error process exited while connecting to monitor: qemu-system-x86_64: -drive file=/home/rjones/d/libguestfs/.guestfs-1000/root.2801,if=none,id=drive-scsi0-0-1-0,format=raw,cache=unsafe: could not open disk image /home/rjones/d/libguestfs/.guestfs-1000/root.2801: No such file or directory This file *does* exist. libvirt (or something) just cannot "see" it for some reason. This state persists until the user libvirtd program is killed, and then everything starts working again. Version-Release number of selected component (if applicable): libvirt-0.10.0-1.fc19.x86_64 How reproducible: Happened twice so far, on two separate days. Steps to Reproduce: 1. Unknown, but keep starting up libguestfs and you'll hit it eventually.
I'm going to put this down to the buggy libvirt 0.10.0 release. Certainly libvirt from git nor libvirt 0.10.1 seems to suffer from this any more.