Comment # 12 on bug 1174365 from Klaus Mueller

A completely other example:
Given is a standard KDE session (normal user is logged in). In the KDE konsole,
a VM is started with "virsh start VM". The VM itself doesn't have any graphical
window (-> no SDL configured). The only way to reach this VM is via net or vnc.
If you end this KDE session (logout), the VM continuous - isn't stopped. That's
expected and ok. The VM completely runs outside of a systemd service
definition.
If you now restart the host via systemctl reboot or maybe do a shutdown via
systemctl, the VM is suspended, too.
Iow: there must be a way, how libvirtd is informed about the shutdown / reboot
- of the host independently of a systemd service definition. This way seems to
be used always - even if there is service definition, which cares about running
VMs.