Home Assistant restarted but I did not ask it to

How do I figure out why Home Assistant restarted itself when I did not trigger it?
It’s happened at least twice now in the last month.

Have you gone through your log files? While you can do this in the UI, I personally find it easier to load the home-assistant.log into my favorite text editor (BBEdit) so I can easily search and scroll.

It happened twice so far today (it’s now 14:45).
homeassistant.log.1:

2023-12-29 11:51:51.329 ERROR (MainThread) [homeassistant.helpers.entity] Update for sensor.front_smart_timer_battery fails
2023-12-29 12:18:42.877 WARNING (MainThread) [homeassistant.helpers.entity] Update of sensor.network_scanner is taking over 10 seconds
2023-12-29 12:51:59.934 WARNING (MainThread) [custom_components.fordpass]
2023-12-29 12:51:59.935 WARNING (MainThread) [custom_components.fordpass] Error communicating with FordPass for 3FMTK3SU5NMA51454
2023-12-29 12:51:59.935 WARNING (MainThread) [custom_components.fordpass] Returning Stale data to prevent unavaliable status

and homeassistant.log does not show anything:

2023-12-29 13:20:12.733 WARNING (SyncWorker_0) [homeassistant.loader] We found a custom integration pyscript which has not been tested by Home Assistant. This component might cause stability problems, be sure to disable it if you experience issues with Home Assistantssistant. This component might cause stability proble
2023-12-29 13:20:12.736 WARNING (SyncWorker_0) [homeassistant.loader] We found a custom integration localtuya which has not been tested by Home Assistant. This component might cause stability probl
2023-12-29 13:20:12.738 WARNING (SyncWorker_0) [homeassistant.loader] We found a custom integration sun2 which has not been tested by Home Assistant. This component might cause stability problems,
2023-12-29 13:20:12.741 WARNING (SyncWorker_0) [homeassistant.loader] We found a custom integration thermal_comfort which has not been tested by Home Assistant. This component might cause stability
2023-12-29 13:20:12.736 WARNING (SyncWorker_0) [homeassistant.loader] We found a custom integration localtuya which has not been tested by Home Assistant. This component might cause stability problems, be sure to disable it if you experience issues with Home Assistant

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There really isn’t enough information there to know what the issue is, unless it’s either one of the extensions you listed or it could be your drive going out. Given the history stats you posted, it’s certainly not at a particular time so unlikely to be some sort of automation that’s running.

Which flavor of HA are you running? What device? rPi? SD card? SSD? VM?

You can try removing integrations. I would guess whatever error was logged last before a restart (so likely the last entry in the .1 log) would be the first place to start.

It’s Home Assistant OS on an HA Blue (ODROID-N2+). My newest integration is the Nmap Tracker. I was scanning 192.168.1.0/24 but have now reduced it to 192.168.1.150-192.168.1.199 as it could have been overtaxing something. The other thing I noticed is log.1 stops at 12:51.59 but sensor.system_started shows that session was from 7:18:28 until 1:20:38 which further indicates a possible resouce issue.

HA has been up for 2-1/2 days now so it looks like Nmap Tracker for 192.168.1.0/24 likely was the issue.
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