说明：  让系统开机、关机运行程序的源码，运行一次后无需调用本身，也无需调用其他程序，可以让系统在开机关机时候自动运行程序。这里给出的范例是让系统自动记录开关机时间。
(Let the system reboot, shutdown of the source code running the program, run once without calling itself, but also the need to call other programs, you can let the system automatically shut down during the boot run the program. Examples given here is to let the system automatically records the time switch machines.)