[ntp:questions] NTP no internet connection

Steve Kostecke kostecke at ntp.org
Sun Feb 10 03:59:22 UTC 2008

On 2008-02-09, flyersix <mhanntest at yahoo.com> wrote:

> I have a network that I would like to cordinate the time in without
> exposing it to the internet for NTP servers.

What level of time stability are you looking for?

> Could I just setup NTP on one of my internal servers and set the
> clients to go to it for time syncs? I know the time won't match the
> internet time

ntpd does not synchronize to "internet time."

ntpd synchronizes computer clocks to a common timebase over networks;
the ubiquitous, and cheapest, timebase is UTC.

ntpd accomplishes this synchronization by steering, or disciplining, the
system clock to bring it as close as possible to the best estimate of
the common timebase.

> but my thought is if I only need to change the time on the one server
> and then let the clients all go to it to update their time.

You can use ntpd for this purpose. Here's what you do:

1) Choose the system with the most stable clock to be the master clock
for your time island

2) Configure your master and the clients as follows:


# Server ntp.conf:

# The ntpd user must be able to write to this drift file
driftfile /path/to/ntp.drift

# maxpoll 2 allows this ntpd to be ready to serve clients within
# 60 seconds of start-up.
server maxpoll 2


# Client ntp.conf:
driftfile /path/to/ntp.drift
server your.master.ntpd iburst


3) Set the master clock by your wrist-watch and _then_ start ntpd, with
'-g', on the master and the clients

Once the master has drifted "far enough" from wrist watch time use the
following steps to correct it:

1) Stop ntpd on the master

2) Reset the system clock (not the RTC) from your wrist watch

3) Start ntpd on the master

You can improve the stability of the master clock by temporarily
providing that ntpd a real timebase (either with a radio clock or via a
network) and allowing ntpd to run long enough to calculate the frequency
correct needed to keep your clock stable. Ideally the ambient conditions
and system load for the server will be the same as your production

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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