-c：取消前一次关机命令
-h：关机
-r：重启 

[root@localhost tmp]# date
Sat Jul 15 09:28:35 CST 2017
[root@localhost tmp]# shutdown -r 05:30
Shutdown scheduled for Sun 2017-07-16 05:30:00 CST, use 'shutdown -c' to cancel.
[root@localhost tmp]# shutdown -r 05:30 &
[1] 4936
[root@localhost tmp]# Shutdown scheduled for Sun 2017-07-16 05:30:00 CST, use 'shutdown -c' to cancel.
 
Broadcast message from root@localhost.localdomain (Sat 2017-07-15 09:30:00 CST):
 
The system is going down for reboot at Sun 2017-07-16 05:30:00 CST!
 
^C
[1]+ Done shutdown -r 05:30
[root@localhost tmp]# shutdown -c
 
Broadcast message from root@localhost.localdomain (Sat 2017-07-15 09:31:03 CST):
 
The system shutdown has been cancelled at Sat 2017-07-15 09:32:03 CST!

halt
init 0
poweroff 

reboot
init 6
 

runlevel
cat /etc/inittab

logout

[root@localhost tmp]# 
[root@localhost tmp]# runlevel
N 5
[root@localhost tmp]# init 3
PolicyKit daemon disconnected from the bus.
We are no longer a registered authentication agent.
[root@localhost tmp]# runlevel
5 3
[root@localhost tmp]# logout