FortiGate-901G v7.4.3 build2573 Fortigate had experienced an unexpected power off!

Did you get a log message?
Have you confirmed if you had a power outage?

Hello kitti1,

Hope you are doing well!

This message will be reported by FortiGate once the device is powered back on.
If FortiGate has rebooted unexpectedly, this message may also be logged.

It's probably because unlike a reboot when the FGT lost power it couldn't record anything by software like a time stamp because power was lost. Then when it came backup it gathered information from hardware as much as possible for what might have happened. But for the reason above the time stamp was not the part of info it was able to gather.

If it's in a-p HA, you can know when an a-p swap happens as the result of the down primary. But if it's a stand-alone and if you or someone was not there to experience the down in person, you wouldn't be able to tell exactly when it went down only based on the device's event log.

To troubleshoot an unexpected power-off issue on a FortiGate device, you can follow these steps:

1. Check the power source: Ensure that the power source to the FortiGate device is stable and not experiencing any fluctuations or interruptions.

2. Power supply units: Verify that all power supply units (PSUs) are properly connected and functioning. In case of a failure, replace the faulty PSU with a new one.

3. Check for overheating: Make sure the device is not overheating. Ensure proper ventilation and cooling mechanisms are in place.

4. Review logs: Check the system logs on the FortiGate device to see if there are any error messages or warnings related to the unexpected power off event.

5. Hardware inspection: Inspect the device for any physical damage or loose connections that could be causing the power off issue.

6. Check the crash logs with the help of the command: dia debug crash log read

You can also use the COMLog feature and wait for the issue will happen again to discover why the FortiGate was rebooted. Please refer to the below docuent for more information:

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Understanding-the-log-message-FortiGate-had/ta-p/228082#:~:text=The%20message%20will%20be%20reported,why%20the%20FortiGate%20was%20rebooted.

Do a console and wait for it to reboot and check the logs which come, could be a kernel panic.