????????????
????1??reboot
????2??shutdown -r now ????????(root??????)
????3??shutdown -r 10 ??10???????????(root??????)
????4??shutdown -r 20:35 ??????20:35???????(root??????)
???????????
????1??halt   ??????
????2??poweroff  ??????
????3??shutdown -h now ??????(root??????)
????4??shutdown -h 10 10???????????