shutdown command broadcasts a message to other system users as shown in the screenshot below:
# shutdown 13:25
Linux Shutdown Broadcast Message
Shutdown scheduled for Fri 2017-05-12 13:25:00 EAT, use 'shutdown -c' to cancel. Broadcast message for root@ucartz (Fri 2017-05-12 13:23:34 EAT): The system is going down for power-off at Fri 2017-05-12 13:25:00 EAT!
To send a custom message to other system users before an inline shutdown, run the command below. In this example, the shutdown will happen after two minutes from the time of command execution:
Supposing you have certain critical system operations such as scheduled system backups or updates to be executed at a time the system would be down, you can cancel the shutdown using the
-c switch as shown below and initiate it at a later time after such operations have been performed:
# shutdown -c
Linux Shutdown Cancel Message
Shutdown scheduled for Fri 2017-05-12 14:10:22 EAT, use 'shutdown -c' to cancel. Broadcast message for root@ucartz (Fri 2017-05-14 :10:27 EAT): The system shutdown has been cancelled at Fri 2017-05-12 14:11:27 EAT!
# shutdown 2 The system is going down for required maintenance. Please save any important work you are doing now!