[GTALUG] mysterious restarts

[D. Hugh Redelmeier]

We have a computer that started doing random and frequent restarts on the 
weekend.  We don't know why.

Any suggestions?

It looks as if the power dips momentarily and the computer reboots,
with no message that we have observe.  But it could just as easily be
a crash of some other kind that leaves no trace.

The system is an HP Compaq Pro 6300 Small Form Factor PC running
Fedora 20.

The crash seems to be at different points (i.e. not one consistent
software activity).  The crashes don't seem correlated with heavy
workloads (eg. it crashed a couple of times while I was staring at log
files to see if there was any hint of the problem).

Hypothesis: a Fedora 20 bug.  But the software has not been changed in
months.  Updates have not been appled this year.  Since the behaviour
has changed without the software changing, I don't think that Fedora
is to blame.

Hypothesis: it might be heat-related (the room it is in gets warm).  I
vacuumed out the interior and defuzzed the heat sinks.  This did not
improve the uptime.

Hypothesis: it might be contact-related.  So I disconnected and 
reconnected most internal connectors and reseated the memory.
This did not seem to improve the uptime.

Hypothesis: it might be the power supply.  Normally, I'd swap power
supplies to test this hypothesis but this Small Form Factor computer
has a unique (and probably expensive) power supply.  I opted to move
the disk to a Dell OptiPlex 990 Small Form Factor computer and use that.

The Dell, with the HP's disk, seems stable.  No rebooting.  This is in
the same warm room, but the weather has changed.

In the original HP box, I installed a disk that I had laying around (a
60G drive from a discarded laptop), installed Ubuntu 16.04, and have
been running four CPU-bound processes for 24 hours.  No crash.  I
admit that this is in a cooler room.  The heat and power load of a
laptop drive is less than that of a 3.5" HDD, but I would not think
that that is significant.

The computer is a couple of years old but still has a year of
warranty.  There are confidential files on the disk drive so I'd like
to narrow down the problem before calling in HP support.  Asking for a
particular replacement part is more convenient that shipping the
computer back to HP.