[ntp:questions] What is the mean of below output?

William Unruh unruh at invalid.ca
Mon Aug 6 21:52:20 UTC 2018


On 2018-08-06, David Woolley <david at ex.djwhome.demon.invalid> wrote:
> On 06/08/18 08:16, ashishchugh.org at gmail.com wrote:
>> 3- Is there is any way through i can determine that what is the currently difference between my local system and ntp server.
>
> No.  If you could, NTP could modify the local time to make the value zero.

That is of course what it tries to do, without jumping the local time (which
would be bad). Of course the whole chain (Your program, your network hardware,
the network, various routers etc along the way, the remote machine hardware,
the remote software and back again) introduces noise, so you do not know that
the remote ntp server's time is. But in the logs it will tell you what the
difference is between the local time and the estimate of the remote time is
obtained from that noisy chain. That is the best you can do. 
Of course you could attach your ssytem to gps, and get the remote gps server's
time to 10s or 100s of nanosecond accuracy. And yo ucould use that to see how
far your system is off the remote server, If you could borrow a gps, you could
test your system. If you bought a gps, then the best idea would be to use it
as your server, and get your machine disciplined to sub microsecond accuracy.
 
 From network servers, you can expect 10s of microseconds (nearby servers--
 like in the same  building) to millisec for distant servers. 
For gps, it depends on how you feed the gps into your system. Here you can get
100s of nanoseconds to a few microseconds using chrony. 



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