Re: Easy NTP Time Server question for the experts out there.

On Thu, 01 Dec 2005 09:47:43 +0100, Jeroen Jonk took a five-minute break
from flipping burgers to boot the etch-a-sketch and scribble out:

> MarkH wrote:
>
>> I want to setup my server to automatically check the time on an NTP
>> server and update its clock. Checking once every couple of hours would
>> do nicely.
>>
>> I have googled and found way too much information, but have edited my
>> /etc/ntp.conf file to include a server (nz.pool.ntp.org) and have been
>> able to set the time from the command prompt with the ntpdate command.
>>
>> I am just not sure what command to use to get the PC to automatically
>> check the time using the ntp.conf settings, or how to set it to
>> checking at
>> regular intervals. The commands that I found with my google search
>> just gave me errors due to being for different versions of SUSE or
>> different distros, but this must be an easy question for some of you to
>> answer.
>>
>> Assuming ntp.conf is correct what command do I use for setting the time
>> at regular intervals?
>>
>>
> YaST --> Network Services --> NTP Client.
>
>
Exhaustive research, there. :)

Actuallly Yast's NTP client doesn't have a config for checking on
intervals.

http://www.perfectreign.com/modules/articles/article.php?id=4


>From the MAN page:

By default, ntpd runs in continuous mode where each of possibly several
external servers is polled at intervals determined by an intricate state
machine. The state machine measures the incidental roundtrip delay jitter
and oscillator frequency wander and determines the best poll interval
using a heuristic algorithm. Ordinarily, and in most operating
environments, the state machine will start with 64s intervals and
eventually increase in steps to 1024s. A small amount of random variation
is introduced in order to avoid bunching at the servers. In addition,
should a server become unreachable for some time, the poll interval is
increased in steps to 1024s in order to reduce network overhead.

In some cases it may not be practical for ntpd to run continuously. A
common workaround has been to run the ntpdate program from a cron job at
designated times. However, this program does not have the crafted signal
processing, error checking and mitigation algorithms of ntpd . The -q
option is intended for this purpose. Setting this option will cause ntpd
to exit just after setting the clock for the first time. The procedure for
initially setting the clock is the same as in continuous mode; most
applications will probably want to specify the iburst keyword with the
server configuration command. With this keyword a volley of messages are
exchanged to groom the data and the clock is set in about a minute. If
nothing is heard after a couple of minutes, the daemon times out and
exits. After a suitable period of mourning, the ntpdate program may be
retired.

When kernel support is available to discipline the clock frequency, which
is the case for stock Solaris, Tru64, Linux and FreeBSD, a useful feature
is available to discipline the clock frequency. First, ntpd is run in
continuous mode with selected servers in order to measure and record the
intrinsic clock frequency offset in the frequency file. It may take some
hours for the frequency and offset to settle down. Then the ntpd is
stopped and run in one-time mode as required. At each startup, the
frequency is read from the file and initializes the kernel frequency. POLL
INTERVAL CONTROL
This version of NTP includes an intricate state machine to reduce the
network load while maintaining a quality of synchronization consistent
with the observed jitter and wander. There are a number of ways to tailor
the operation in order enhance accuracy by reducing the interval or to
reduce network overhead by increasing it. However, the user is advised to
carefully consider the consequenses of changing the poll adjustment range
from the default minimum of 64 s to the default maximum of 1,024 s. The
default minimum can be changed with the tinker minpoll command to a value
not less than 16 s. This value is used for all configured associations,
unless overriden by the minpoll option on the configuration command. Note
that most device drivers will not operate properly if the poll interval is
less than 64 s and that the broadcast server and manycast client
associations will also use the default, unless overriden.

In some cases involving dial up or toll services, it may be useful to
increase the minimum interval to a few tens of minutes and maximum
interval to a day or so. Under normal operation conditions, once the clock
discipline loop has stabilized the interval will be increased in steps
from the minumum to the maximum. However, this assumes the intrinsic clock
frequency error is small enough for the discipline loop correct it. The
capture range of the loop is 500 PPM at an interval of 64s decreasing by a
factor of two for each doubling of interval. At a minimum of 1,024 s, for
example, the capture range is only 31 PPM. If the intrinsic error is
greater than this, the drift file ntp.drift will have to be specially
tailored to reduce the residual error below this limit. Once this is done,
the drift file is automatically updated once per hour and is available to
initialize the frequency on subsequent daemon restarts.

--
kai
www.perfectreign.com

linux - genuine windows replacement part
.

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