[ntp:questions] Re: limitation on the client time/date at ntp startup

David Woolley david at djwhome.demon.co.uk
Wed Aug 23 06:49:04 UTC 2006


In article <1156282058.994857.239810 at p79g2000cwp.googlegroups.com>,
"BG" <brenda.gillcrist at navy.mil> wrote:

> Thank you. The reason I need to change the client clock is to 'prove'
> to skeptics that it is working.

But it doesn't prove that it is working.  All it demonstrates is 
an error recovery path, working at a precision that could be achieved
using very crude time synchronisation protocols, is working.  If you
really want to demonstrate that ntpd is working, you would need to do
something like heating or cooling the crystal oscillator on the
motherboard (assuming you are in an air conditioned room and can't
do this for the whole machine) and demonstrate that the frequency error
is compensated correctly.

In reality, ntpd has no need to be able to handle errors of more than
about 30 seconds, as that is about the maximum error in a watch used to
set the initial time.

> BG wrote:
>
> > What is the limitation on the time difference of a client clock at ntp
> > startup? Is it 1000 sec? Is there an option to increase this or a

It's unlimited if you use the -g option, but only for the first
correction.

> > 'commercial' version of NTP that will allow greater differences? e.g.
> > years

The reference version is much easier to change in this respect than any
commercial version, as you can just change the limit constant in the
source code.  You don't even need to change the source code, as there is
a tinker option documented that allows you to change or disable this
check.

However, make sure that you change it back after the admirals
have left.

> > distributes the time to another pc on the network. It appears that I
> > can not change the client pc time/date more than 1000 sec or ntp will
> > not correct the client clock.

This is not startup, though.




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