Xorg.0.log stuck, never stops

[Adam Nielsen]

> Because its also a devel machine, haveing 2 SSD's attached where it can 
> build the target sw, there are often 1 minimum to as high as 4 ssh -Y 
> logins. But only one in the last several days.

SSH wouldn't do it, but anything that runs on a timer could.  For
example if you have DPMS power saving to shut off the monitor after a
few minutes, then when it wakes up again it may query the monitor so
that it can set the correct screen resolution again.

If you're running a full desktop environment (as opposed to a basic
install) then there are many things it could be.  If you're running a
minimal Linux distro with a cut down Xorg install then power saving is
about the only thing that could be on by default that might do this,
that I can think of, not counting hardware issues/bad cables which you
say aren't a problem given the lack of display issues.

> I do not know that to be the case but if a part was 
> being carved at the time, I'd imagine it would be damaged as this 
> nominally 5 milliseconds means the machine is un-monitored for a part 
> wrecking way too long.

This won't stop the system for five milliseconds, it will take five
milliseconds for the process to complete but other programs will
continue to run in the background.

However if your lathe control software is that critical with timing,
then it should be running with its priority set to "realtime" so that
it takes priority over all other programs anyway.  Otherwise anything
could hold it up - e.g. random disk cache flushes.

The timestamps are exactly 30 minutes apart down to the second, which is
a common value for power saving options, so I'd start looking there.

Power saving is one thing that can disrupt running processes because
some devices take enough time to respond to wake up events that the
system really can be completely blocked for a few milliseconds, so in
your case where you need code running every millisecond to monitor
external hardware, I'd be inclined to disable any power saving options
I could find, including those in the kernel relating to CPU throttling,
USB devices, etc.

Cheers,
Adam.