Sort of off topic, raspi shutting down

General
1

Sorry, and yes it may be better I ask in a RasPi forum.

Story:

Raspberry Pi 3 Model B Plus Rev 1.3

PRETTY_NAME="Raspbian GNU/Linux 10 (buster)"
NAME="Raspbian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=raspbian
ID_LIKE=debian

Buster
NR 3.0.2

It has an argon fan hat on it.

Two Three times now I've come home and the machine is/has shut down.

First time: well, it was the first.
The machine is using a name brand power supply.
(Been through power problems before)

Second time: Had a good long up time.
Uptime 19 weeks.
Accidentally pressed the button on the hat wrongly. (Long press rather than short press)

Third time:
The other night.
Uptime 3 weeks 6 days.
If the machine overheats it broadcasts a message informing me of the shutdown and reason.
Nothing detected on overheating.
And it was close to midnight and I was tired.

For when it next happens and I hope it is not late:
Where do I look to see the reason for the shutdown?

I know this is page 1 for ubuntu people.
I'm still not one of them.

Thanks.

2

Indeed better a question for a rapsberry forum.
Look in /var/log/syslog, backtrack to the previous boot

3

These can also fail Andrew!

4

Thanks both.

Shall have to do more digging.

The swap file has been suggested too.