To schedule a system shutdown in 30 minutes from now

$ sudo shutdown +30

To shutdown the system immediately

$ sudo shutdown now

To shutdown the system in 30 minutes from now and notify the users with message “system upgrade” 

$ sudo shutdown +30 "system upgrade"

To halt your system

$ sudo shutdown -H

To make shutdown power-off machine

$ sudo shutdown -P

To reboot using shutdown

$ sudo shutdown -r

To specify a time argument and a custom message

$ sudo shutdown -r +10 "system upgrade"

To cancel a scheduled shutdown

$ sudo shutdown -c

 To cancel a scheduled shutdown, and to broadcast a message to all users

$ sudo shutdown -c "reboot is cancelled"

regards,

T.Dhanasekar