10.7.2. How Does It Work?

Xen boots a small program called a hypervisor before booting Domain-0 . The hypervisor masks the underlying hardware and presents a modified virtual environment to each domain. Domain-0 has direct access to certain hardware, such as network interface cards and other peripherals, and the standard device drivers are used to access those devices.

Inside Domain-0 , a service daemon named xend provides monitoring and control functions for the guest domains and communication between the guest domains and certain types of hardware (such as network interfaces).

The Xen environment is different from the normal PC environment, and the operating system must be modified to run in this special environment; this is called paravirtualization because it requires some cooperation on the part of the guest operating system. The advantage to this approach is higher performance and the ability to control the guest operating system in certain ways (such as sending the guest OS a shutdown message when xm shutdown is used).

Xen is developed as an open source project; XenSource is a company formed by the original Xen researchers to offer an enhanced, commercially supported version of Xen.

The Fedora Xen guest installation tool, xenguest-install , is a Python script that interfaces with Fedora's Anaconda system and python libraries. The configuration files generated by xenguest-install are stored in /etc/xen.