Clock on compute nodes

[Artur Dubrawski]

You never know what you are going to get when you ask a sysadmin to please
fix a computer clock :)

Thanks Predrag and Emre.
Artur

On Wed, Dec 12, 2018 at 2:58 PM Predrag Punosevac <predragp at andrew.cmu.edu>
wrote:

> Emre Yolcu <eyolcu at cs.cmu.edu> wrote:
>
> > Hi Predrag,
> >
> > This is a very minor annoyance, so feel free to ignore if you're busy.
> > Somebody brought up before that time was set incorrectly on some compute
> > nodes. For instance, it seems gpu9 is 3 minutes ahead of Pittsburgh time,
> > and gpu8 is 9 minutes ahead. When you have time could you check whether
> the
> > sync is working correctly?
>
> Fixed! Thank you so much for the report. Clock drifting is not a minor
> issue and it is very serious security problem and the best indication of
> failing hardware. Unfortunately CMU School of Computer Science is
> blocking NTP protocol so I run two internal NTP servers which
> synchronize time via HTTP protocol as well some other tricks. In this
> particular instance the culprit(s) were dead chronicd clients on GPU8
> and GPU9 machines. I fixed them now.
>
> It is also interesting to remind everyone how General Theory if
> relativity affects our computing infrastructure. The biggest scientific
> leap General Relativity Theory made was abandoning the concept of
> absolute time. Absolute space concept was abandoned already in special
> theory of relativity. The concept of absolute space-time was introduced
> by Isaac Newton in order to preserve Galilean principle of relativity
> which was supposed to be 4th Newton's law (originally he wanted to have
> 6 before reducing to three). One may refer to Arnold's Mathematical
> Methods of Classical Mechanics to learn about those delicate points.
> Most graduate text in physics a mute about those points which makes them
> irrelevant.
>
> Only Poincare was able to demonstrate invariance of law's of nature
> without Galilean principle of relativity thereby giving a major
> push to Theory of Relativity.
>
> Long story short time depends on the inertial frame which means that no
> two computers have the same time. Clock synchronization is essentially
> averaging in order to enable us to work on the network.
>
> Cheers,
> Predrag
>
>
> >
> > Best,
> >
> > Emre
>
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