When I made my first Centos 6 install on a Debian based Xen, the installation procedure hangs. I found the solution in this mailing list post: [xen-tools-discuss] Centos 6 installs hang
If it’s the same issue as I’ve enconterer, in 20-setup-yum, you need to change line 36 to “chroot ${prefix} /usr/bin/yum update -y”. Yum wait for your input and it should not.