kvm 建立子镜像（复制镜像）

kvm-img create -b ubuntu-server.img -f qcow2 server1.img 

Formatting 'server1.img', fmt=qcow2 size=5368709120 backing_file='ubuntu-server.img' encryption=off cluster_size=65536 

kvm -m 1000 -drive file=server1.img,if=virtio -smp 1,4 -k en-us