Apparently, my unraid box recovered from an unexpected shutdown, as if someone cut the power lead (which noone did). This could mean two things.

 

1. Unlikey, but a power outage may have lasted long enough to drain the UPS, and unraid didn't honour the shutdown settings while running on UPS battery.

2. More likely, the server crashed itself and got itself to reboot automatically. But crashed because of what...?

 

In either case, I don't know where to find out more. I can't find a log for the UPS. I would like to know a date+time of the last outage, or the last outage X seconds ago. Either would be helpful, but I don't know where to get this information. It's an APC Back-UPS ES 550G, connected via USB.

 

I also can't find information on what happened before the unexpected reboot. The server log seems to have been cleared during startup, which is extremely bad practice if this was deliberate. The damage (if any) is already done, so enabling persistent logs is of no use now. More so because I have no way of knowing how to reproduce the problem - I don't even know where to start, it could be literally anything, so far.

 

At any rate, where can I find logging information from before the crash?

 

PS, the reason scenario 2 is more likely, is because other UPS's in the house didn't indicate an outage either, although I'm not sure how good they are at reporting them. My NAS survived the outage if there was one, so that's an indication. I wasn't around to experience it myself, unfortunately.

If there is nothing in the  logs folder, you can't.

 

I would suggest that you install the Fix Common Problems  plugin and turn on the 'Troubleshooting  mode'.  Then wait until it happens again.  You should then find what you are seeking in the  logs folder. 

You also forgot two more premises.  (1) The power went out and the battery in the UPS failed to carry the load until unRAID could get shutdown.  (2) The power rating of the UPS was momentarily exceed as all of the HD's spun up and the UPS shut itself down.

 

Those two additional scenarios are highly unlikely.

1) My UnRAID box never takes more than a minute or so to reboot. So shutting down is a matter of seconds.

2) I don't have spinning harddisks

 

 

So anyway, what is the reason UnRAID by default throws away logs? Especially in case of an unclean shutdown, it should be smart enough not to clean out the logs!

The logs are actually stored in a RAM disk.  Something has to copy them off to a device (Flash Drive or HD) for them to be preserved to survive reboot or power shutdown.  unRIAD was designed to run from the RAM disk so as not to be continuously writing to the Flash Drive as those continual writes would cause the drive to fail within a short period of time. 

 

You can install the 'Fix Common Problems' plugin and turn on its 'troubleshooting mode' to do what you want to do.  That is what I would suggest that you do next.