command line

nova reboot [Instance]

It is equivalent to

virsh reboot
是优雅的重启, 为何build image时要安装acpid ,就是为了实现这个，参见下面的Install the ACPI service

nova reboot --hard  [Instance]

It is equivalent to

virsh destroy

Install the ACPI service¶

To enable the hypervisor to reboot or shutdown an instance, you must install and run the acpid service on the guest system.

Log in as root to the CentOS guest and run the following commands to install the ACPI service and configure it to start when the system boots:

 yum install acpid
 systemctl  enable  acpid

build an image manulally