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I have an Asus P8B-M motherboard that has been in use for several years. It is now randomly stopping operation several hours after booting; as in just suddenly stopping all CPU operation. It is running a current Ubuntu server Linux. No hardware changes have been made to the system for months prior to this. Memory test did not uncover any errors. Reseated all the cables, memory, and two PCI cards.

The BIOS syslog has entries that show 

Sensor Number: 0x17 Reserved or Unknown
Event Description: Record Type 0x02, Assertion Event, Channel Number 0x 0.

It has some hex values displayed: 

71 2 2 DE E7 CB 5A 88 0 4 DC 17 75 A0 4 0

Is there any way to know what that error means? I have been unable to find information about it by searching. The Linux logs do not show any unusual errors; they just stop at the moment the system locks up. The BIOS syslog entries do NOT show up EVERY time the system locks up, though.

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If I recall correctly, the sensor at address 0x17 is usually a DIMM sensor. That would suggest you have a stick of RAM on its way out, which would also make sense given your symptoms. Try booting the machine with only one RAM stick, see if the problem recurs, etc...then try any others, one at a time. If the machine parks on you with certain RAM installed, you found your culprit.

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  • it was a good idea, but both sticks,one at a time, still see the lock up. I don't see the syslog entry with every lockup, though. – simpleuser Apr 10 '18 at 0:06
  • also tried moving one stick into different sockets, with no improvement – simpleuser Apr 10 '18 at 2:02
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    Then it may be the sensor itself, in which case it's time to look for a new mobo. Unfortunately, that's a server motherboard and those things aren't cheap. The good news is, I've seen em hit E-Bay for about 80 bucks. Still, if you're using a processor that can drop in another board (since that one is LGA1155) and aren't using ECC RAM, you may want to take the "any old mobo" approach for something that old. – CDove Apr 10 '18 at 11:50
  • Thank you for all the ideas and info. In the end, I believe the MB is bad; I can run (stable? but with all secondary services disabled due to low memory: only apache, mysql, mail, & antispam) if I use only 4MB of memory and I don't access the BIOS during the boot. If I break either of those rules, then the system locks up at some point. – simpleuser Apr 12 '18 at 17:57

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