You are using libvirt on Centos 6 and you need to boot a virtual machine from a CD

Edit the virtual machine

virsh edit domainname

Find the section “<os>” and add the following line at the top of the section

<os>
   <boot dev='cdrom'/>
   .....
</os>

Find section “<devices>” and add the following section

<devices
 <disk type='file' device='cdrom'>
     <source file='/var/lib/libvirt/images/CentOS-6.4-x86_64-minimal.iso'/>
     <target dev='hdc'/>
     <readonly/>
   </disk>
  ....
</devices>

Replace “/var/lib/libvirt/images/CentOS-6.4-x86_64-minimal.iso” with the iso image you want to boot. Note if there is another <target dev=’hdc’/> then replace the value above with <target dev=’hdd’/> or the next letter available.