The communication between the virtualization solutions (KVM, Xen, LXC) and the libvirt API is managed by the daemon libvirtd. It needs to run on the VM Host Server. libvirt client applications such as virt-manager, possibly running on a remote machine, communicate with libvirtd running on the VM Host Server, which services the request using native hypervisor APIs. Use the following commands to start and stop libvirtd or check its status:

tux > sudo systemctl start libvirtd

tux > sudo systemctl status libvirtd
libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled)
Active: active (running) since Mon 2014-05-12 08:49:40 EDT; 2s ago
[...]

tux > sudo systemctl stop libvirtd

tux > sudo systemctl status libvirtd
[...]
Active: inactive (dead) since Mon 2014-05-12 08:51:11 EDT; 4s ago
[...]

To automatically start libvirtd at boot time, either activate it using the YaST Services Manager module or by entering the following command:

tux > sudo systemctl enable libvirtd

Important: Conflicting Services: libvirtd and xendomains

If libvirtd fails to start, check if the service xendomains is loaded:

tux > systemctl is-active xendomains
active

If the command returns active, you need to stop xendomains before you can start the libvirtd daemon. If you want libvirtd to also start after rebooting, additionally prevent xendomains from starting automatically. Disable the service:

tux > sudo systemctl stop xendomains
tux > sudo systemctl disable xendomains
tux > sudo systemctl start libvirtd

xendomains and libvirtd provide the same service and when used in parallel may interfere with one another. As an example, xendomains may attempt to start a domU already started by libvirtd.