[ntp:questions] Re: NTP sync on a standalone network (Windows 2k)

Paul.Croome at softwareag.com Paul.Croome at softwareag.com
Fri Aug 18 09:51:27 UTC 2006


Alexandre Carrausse schrieb:

> I am still not getting the purpose of this file. Is the value inside this
> file supposed to change? Or is this value configured by someone for good.
> Should I become worried if I see some strange values in those files?
> What is the meaning of a high value? Is it good or bad if the value is
> 0.000?
>

The ntp.drift file stores the frequency error of the local system
clock, as compared
to the True Frequency (1 second per second) as defined by reference
clock sources
or external, higher-stratum NTP servers. It's used if NTP is stopped
and
restarted for any reason, so that NTP has a good idea of what the
system clock
frequency error might be and can concentrate on correcting phase error.
The frequency error of the local system clock varies due to temperature
changes
and ageing, therefore NTP stores a new value in ntp.drift periodically
(once per
hour according to the documentation). You don't normally have to touch
it --
it all happens automatically.

Read more about this here:
http://www.eecis.udel.edu/~mills/ntp/html/debug.html.

At the moment, my five NTP servers (all Sun SPARC hardware)
have the following values in their ntp.drift files:
-93.879
-22.856
13.594
-54.257
2.227

What do you mean by 'strange values'?

A high value (modulus) means that the free-running frequency of your
system's
local clock is a long way off nominal. A high value is not necessarily
cause for worry;
a value that changes a lot is.

Statistically speaking, it's just about impossible that a real-life NTP
server that's
synchronised to an external time source (UTC) will ever have the value
0.000
in etc.drift. If you see 0.000 under those circumstances, I would bet
that NTP
is not running correctly.

However: If you are running an isolated NTP network with no refclocks
and with
no access to external NTP servers, your highest-stratum server will be
using its
own system clock to synchronize its own system clock, and obviously its
frequency error will be 0.000.

Paul




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