Troubleshooting random shutdowns

[Suiname]

I've been using FreeNAS-8.3.0-RELEASE-x64 (r12701M) for a while now, and it's been pretty great except every once in a while (sometimes months sometimes weeks, kinda random) my system will hang, and be unreachable via web, ssh, etc. Powering off and back on always fixes it until the next time it randomly hangs. I am running it headless, so I can never see what the on-screen output is.

I was wondering what the best way to go about troubleshooting this sort of thing would be. I'm pretty familiar with Ubuntu's kernel, so I tried to use what I know from that, and I've used the dmesg command to see if there are any problems. The only warning messages I see are:
ACPI Warning: Incorrect checksum in table [OEMB] - 0x58, should be 0x57 (2010101 3/tbutils-354)
Trying to mount root from ufs:/dev/ufs/FreeNASs1a WARNING: /data was not properly dismounted

I went to /var/log and looked at the messages file, there doesn't seem to be anything not in dmesg there either, so I'm not sure what's going on here. Any help would be much appreciated.

 

[Dusan]

A reboot wipes all logs, so whatever you see in dmesg or /var/log is not related to the hang.
Your options are to attach a monitor to see if there are any console messages (or maybe the console still works) or configure remote/persistent logging (see the note below table 4.7a for your options).