Xen is the most common hypervisor used on Red Hat Advanced Server 5, Fedora, and distributions based on these, such as CentOS 5. Assuming you are using one of these, to use Xen you must install the xen and kernel-xen packages from your package repository:
# yum install xen kernel-xen
Other operating systems will probably have similar packages. Some offer a groupinstall that will include all the necessary packages:
# yum groupinstall Virtualization
Once installed, reboot your system using the Xen kernel. You may want to modify your /boot/grub/grub.conf file to boot the Xen kernel by default. Usually this means changing the default= entry to default=0, where 0 refers to the first boot configuration described by the file. See Chapter 4 for details on configuring grub and modifying the grub.conf file.
The installation of the previously mentioned packages should also configure two services to run: the Xen daemon (xend) and the xendomains script that the system uses to automatically start and stop your guest domains.
Once the new kernel and xend service is running, you should be able to run the command
# xm list
to list your current nodes. At first you will have one domain running, Domain-0.
To understand Domain-0, it helps to know that your system is not really running Linux directly. It’s running Xen’s own kernel, a virtual machine monitor based on the Nemesis microkernel. Xen’s kernel doesn’t provide an administrative interface; it depends on a modified operating system running as a guest ...