Chapter 10 Install and System Administration for FortiOS 5.0 : Best practices : Shutting down
  
Shutting down
Always shut down the FortiGate operating system properly before turning off the power switch to avoid potential hardware problems.
To power off the FortiGate unit - web-based manager
1. Go to System > Status.
2. In the System Resources widget, select Shutdown.
To power off the FortiGate unit - CLI
execute shutdown
Once this has been done, you can safely turn off the power switch or disconnect the power cables from the power supply.
See Also
Best practices