#Domu

Sometimes you might need to mount a DOMU’s disk in DOM0, so that you can edit files, or even recover them in the event that your DOMU is broken and fails to boot.

For this to work your CPU and motherboard needs to support vt (intel) or amd-v. You can check this by looking at the flags in /proc/cpuinfo. Your looking for either vmx or svm on the flags line.

If you’re doing this from your DOM0 then these flags may not actually show up. Instead type xm info and look for ‘hvm’ on the virt_caps line.

For my hvm install, i’ll be installing Ubuntu 9.04 Desktop Linux.
I have copied the live CD ISO onto my XEN DOM0 and will be installing directly from the iso rather than burning the CD. I have also created a 10GB LVM logical volume to act as the disk for my new DOMU.

If you’ve followed my guide to installing xen from source then you might now be wondering how to create your first VM.
This guide will show you how to manually create and install a VM (known as a DOMU instance in Xen) without any additional tools such as virt-manager, virt-install or virsh. These tools can help the novice, but are quite limiting when it comes to the advance features of xen.

For this example I’ll be installing CentOS5, but this should work for any red-hat based distro (please note there is a bug in fedora10 that stops it booting under xen). This example also uses the paravirtual kernel so it will work even if your CPU does not support AMD-V or intel-VT.

Right, down to business. The first thing we need to do is create a file to user as the hard disk for the DOMU. There are other options for providing hard disks to a DOMU, and I’ll cover some of them in a later guide but for this install I’ll be using a file.

The command below will create an 8GB file that will be used as an 8GB drive. The whole file will be written to disk in one go so may take a short while to complete.
dd if=/dev/zero of=/xenimages/test01/disk1.img oflag=direct bs=1M count=8192