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

David L. Mills mills at udel.edu
Thu Aug 24 21:01:29 UTC 2006


David,

Classic way to test NTP functionality is to stop ntpd, set the time by 
some other means within 68 years of the correct time, then start ntpd 
with -g.

Dave

David Woolley wrote:
> 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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