Kernel, Ramdisk, Root

The values kernel and ramdisk in the configuration relate to the filesystem for Dom 0. If you want to replace the Dom U kernel at a later stage, you can copy the new kernel to the right place in Dom 0 and then just modify the configuration file for the virtual machine.

The vif entry specifies which network interface Dom U is allowed to access and which bridge Xen will use to handle this access. It is also possible to assign a static (arbitrary) MAC address; otherwise, Xen will assign a randomly generated MAC address to the network adapter each time you start the virtual machine. In turn, this will cause Etch's hotplug system to keep changing the network device number, and the automatic configuration in /etc/network/interfaces will then fail.

Guest Filesystems

Two basic options exist for guest filesystems: Either you can assign one or multiple partitions to Xen or the Dom U can work with image files. Both solutions have advantages and disadvantages: Physical partitions typically improve performance, but files allow the administrator to create backups by simply copying from Dom 0.

This decision is a matter of taste and will depend to a great extent on what you will be using the system for. The example in the listing assumes that one Dom U uses /dev/hda3 as a drive for its root filesystem. On top of this, Xen can assign multiple virtual disks as hard-disk partitions to the virtual machine.

Virtual Debian

The guest domain is installed completely from within Dom 0. Theoretically, you could boot the Debian installer with Xen and then use it to install the new system, but in reality, this approach will fail because of the lack of Xen support in the Debian installer kernel. Instead, the Debian Debootstrap [2] installation tool is used. Working as root, type apt-get install debootstrap to install the tool in Dom 0. If you haven't already done so, you will want to install a Linux-compatible filesystem on the target partition for the Linux guest system now. The Dom U will probably need a swap partition too; mk-swap sets this up.