## Install a necessary packages
$ sudo apt-get install kvm cloud-utils genisoimage

## URL to most recent cloud image of 12.04
$ img_url="http://cloud-images.ubuntu.com/server/releases/12.04/release"
$ img_url="${img_url}/ubuntu-12.04-server-cloudimg-amd64-disk1.img"
## download the image
$ wget $img_url -O disk.img.dist

## Create a file with some user-data in it
$ cat > my-user-data <<EOF
#cloud-config
password: passw0rd
chpasswd: { expire: False }
ssh_pwauth: True
EOF

## Convert the compressed qcow file downloaded to a uncompressed qcow2
$ qemu-img convert -O qcow2 disk.img.dist disk.img.orig

## create the disk with NoCloud data on it.
$ cloud-localds my-seed.img my-user-data

## Create a delta disk to keep our .orig file pristine
$ qemu-img create -f qcow2 -b disk.img.orig disk.img

## Boot a kvm
$ kvm -net nic -net user -hda disk.img -hdb my-seed.img -m 512