[ntp:questions] chrony as a server

William Unruh unruh at invalid.ca
Mon Feb 23 21:30:18 UTC 2015


On 2015-02-23, Harlan Stenn <stenn at ntp.org> wrote:
> William Unruh writes:
>> On 2015-02-23, Harlan Stenn <stenn at ntp.org> wrote:
>> > Miroslav Lichvar writes:
>> >> On Sat, Feb 21, 2015 at 07:02:28PM +0000, David Taylor wrote:
>> >> > On 21/02/2015 17:52, William Unruh wrote:
>> >> > []
>> >> > >It will do that too. The crucial item there is "the only method of time
>> >> > >correction is manual entry" which is different from ntpd and orphan
>> >> > >mode. I have no idea why this conversation is continuing. The two are
>> >> > >different. The two methods are trying to solve the same problem
>> >> > >(timekeeping of isolated systems) but doing so in a different manner. I
>> f
>> >> > >you like one better than the other, that is fine. But they are not the
>> >> > >same.
>> >> > 
>> >> > Bill, please enlighten me why I cannot, using NTP's orphan mode, set the
>> >> > time on one PC manually and have another PC sync to it?
>> >> 
>> >> Well, you can, but it's not as easy. You need to find the orphan
>> >> parent first (i.e. the system with the smallest refid), somehow
>> >> figure out its phase and frequency error to the real time, and correct
>> >> them behind ntpd's back (possibly with the date and ntptime -f
>> >> commands).
>> >> 
>> >> With chrony you just run "chronyc -a settime xx:xx:xx" once in a while
>> >> on the server and it will do the rest for you.
>> >
>> > I'm not buying it.
>> >
>> > It's trivially easy to set up a proper orphan mesh.
>> >
>> > A proper network configuration will have multiple time servers on it,
>> > because sometimes things break.  If you want to set up something where a
>> > flock of machines follow a single server, that's your choice and there
>> > are consequences to that choice when things break.
>> >
>> > If you implement the recommended setup then the old local refclock
>> > scheme will usually pretty much just work, and an an orphan scheme will
>> > just work.
>> 
>> Of course it will "work" but the clocks will go wandering off, with no
>> way of hauling them back into time.
>
> Bullshit.  As soon as a proper time source is found the servers will use
> it.

??? That is true in both cases. The assumption was that you have a clock
which has no connectivity for months. Ie, no proper time source will be
found. The question is about disciplining the clock in that case. If
time sources are available, then yes, please use them. 

>
>> Lets start with a single machine
>> with a drift rate of 30PPM. By the end of the month it will be a minute
>> out. So if that is working, then it works. As Lichvar says with chrony
>> you periodically read your watch, or listen to radio, and set the time
>> and chrony figures out that you have a drift rate of about 30PPM and
>> corrects. Now you may not value that possibility, which is perfectly all
>> right, but some people might. 
>
> So you are assuming that an orphan mesh kicks in at a time when there is
> an uncorrected drift of 30ppm, and this is at a site where time synch is
> important and they're OK with no proper time source for a month?

Sure. The computer starts up with no time sources availble. The drift
could well be 30PPm. 

>
> What would happen if chrony happened to lose its time source while there
> was an uncorrected drift of 30ppm?  Anything different?

Yes, you would feed it time manually, and it would use that as its time
source. That is what we are discussing. 

>
> With ntpd and chrony it's possible to adjust the frequency in this case.

It is possible sure. It is just that chrony does it differently. The
question that was raised was whether or not chrony's handling of a time
island is identical with ntpd's. It is not. Now you may not care, or may
not believe anone could be interested in the difference. But they are
different. 

>
> It's posts like these from you that cause me to wonder if you are just a
> troll.  It's why I tend to not respond to you, but sometimes I do
> respond to at least some of your more egregious posts.

??? Clearly you have not been following the discussion. The claim was
that chrony's ability to use manual time input as a time source was
identical with ntpd's orphan or local clock modes. All I have said is
that it is not.  No idea why you call that trolling. 


>
> H



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