Adding Virtualization Support

QEMU / KVM require hardware virtualization support. The first thing to do is to make sure that it is available.

The command will return one line per cpu core if virtualization is enabled. If not, you should first check in the BIOS whether virtualization is disabled.

Libvirt stores its data including the image files of the virtual hard disk(s) for the guest systems in /var/lib/libvirt. If you adhere to the default partitioning layout, the libvirt application data is stored in its own logical volume that you have to create in advance. You need to specify the size of the storage area, a unique name, and the accommodating VG (fedora in case of default partitioning). In the new logical volume, create an xfs file system and mount it at /var/lib/libvirt.

Enable automatic startup at boot and start libvirt.

By default, libvirt creates a (virtual) bridge with an interface virbr0, the IP 192.168.122.1 and the libvirt-internal name as default. In addition, a separate firewall zone libvirt is set up and assigned to the internal interface. Check if everything is running as expected.

The libvirt Fedora installation procedure provides systemd startup scripts that take care of enabling and starting the various unix sockets and services as needed. This includes support for qemu, xen and lxc. Configuration of vbox is disabled by default. The drivers determine during startup whether the required prerequisites are met and abort otherwise. The default services, qemu and lxc in case of Fedora Server, are started at boot time. If not used for about one minute they are deactivated, but will restart on demand as soon as a virtual machine is started (either by command line or Cockpit service). There is no need for administrator intervention at all.

The network configuration is slightly different. The services don’t start at boot time, like qemu, lxc, etc., but on demand at first access. Therefore, you won’t get an interface virbr0 until some libvirt service requests it. That’s sometimes inconvenient, e.g. if you use that interface for non-libvirt services, too (e.g. lxd or nspawn container). You may prefer to enable the virt-network service anyway:

When first used, the list of virtual machines displayed in the center of the page is empty, of course. A box left above that list displays 0 Storage pools. Libvirt uses pools to determine the location of typical files. The installer has already created the directories. Only the pools need to be defined here.

Typically you use one Pool for installation media, stored at /var/lib/libvirt/boot. "Installation media" would be a suitable descriptive pool name. Select 0 Storage pools in the box and then Create storage pool. A new form opens.

If you are logged in as an adminstrative user (even if having used sudo su - ), you are asked to select a connection type, "system" or "session". This selection is presented in various configuration forms, so we explain here. Use "system" for production deployments, the common case. Select "session" in the special case of testing, development, and experimentation. The "session" option does not support any custom or advanced networking, but works pretty much everwhere (including containers) and without any privileges. The libvirt project provides additional information for developers. If you are logged in directly as root, this line doesn’t show up. Instead, everything is treated as system; i.e. production deployment (never do development or experimentation as root).

Next enter "Installation media" as the name, "Filesystem directory" as the type, and /var/lib/libvirt/boot as the target path.

In most cases, the (virtual) hard disk used for a virtual machine is a disk image file stored in /var/lib/libvirt/images. Define another pool named "Disk images" accordingly.

Activate both pools in the drop down menu of each pool.

You may create additional pools as needed, e.g. disk images via iSCSI in a SAN or as a logical volume in a volume group (LVM) on the host’s local disk. The latter offers better performance in theory, but the practical gain is usually rather small, if any. We will not go into further detail here for the time being.

A box on the right above the virtual machines list shows 1 Network and lists the networks managed by libvirt. By default, it contains the internal network default with the interface virbr0. The list does not contain the external interface. It is managed by the server. Nevertheless, it is available for virtual machines.