qemu-img create -f qcow2 centos7-2.img 30G 
qemu-img amend -f qcow2 -o compat=0.10 centos7-2.img 
virsh define centos7-2.xml
virsh destroy
virsh undefine
virsh start centos7-2
virsh edit centos7-2
cat centos7-2.xml

cat zhycentos.xml 
virsh vncdisplay zhycentos

<domain type='kvm'>  
  <name>centos7-2</name>  
  <uuid>d06d7213-9b3d-f32e-f54a-70a82115242e</uuid>  
  <memory unit='KiB'>8388608</memory>  
  <currentMemory unit='KiB'>8388608</currentMemory>  
  <vcpu placement='static'>4</vcpu>  
  <os>  
    <type arch='x86_64' machine='pc'>hvm</type>  
    <boot dev='hd'/>  
     <bootmenu enable='yes'/>  
  </os>  
  <features>  
    <acpi/>  
    <apic/>  
    <pae/>  
  </features>  
  <clock offset='utc'/>  
  <on_poweroff>destroy</on_poweroff>  
  <on_reboot>restart</on_reboot>  
  <on_crash>restart</on_crash>  
  <devices>  
    <emulator>/usr/libexec/qemu-kvm</emulator>  
    <disk type='file' device='disk'>  
      <driver name='qemu' type='qcow2' cache='none'/>  
      <source[color=darkred] file='/home/hao/centos7-2.img'/[/color]>  
      <target dev='vda' bus='virtio'/>  
    </disk>  
    <disk type='file' device='cdrom'>  
      <driver name='qemu' type='raw'/>  
      <source [color=darkred]file='/home/CentOS-7-x86_64-DVD-1503-01.iso'/>[/color]  
      <target dev='hdc' bus='ide'/>  
      <readonly/>  
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>  
    </disk>  
    <controller type='usb' index='0'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>  
    </controller>  
    <controller type='ide' index='0'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>  
    </controller>  
    <interface type='bridge'>  
      <mac address='50:50:18:aa:83:81'/>  
      <source bridge='br0'/>  
      <model type='virtio'/>  
    </interface>  
    <serial type='pty'>  
      <target port='0'/>  
    </serial>  
    <console type='pty'>  
      <target type='serial' port='0'/>  
    </console>  
    <input type='mouse' bus='ps2'/>  
    <graphics type='vnc' port='5909' autoport='no' listen='0.0.0.0'>  
      <listen type='address' address='0.0.0.0'/>  
    </graphics>  
    <sound model='ich6'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>  
    </sound>  
    <video>  
      <model type='cirrus' vram='9216' heads='1'/>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>  
    </video>  
    <memballoon model='virtio'>  
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>  
    </memballoon>  
  </devices>  
</domain>