[ntp:questions] Ntp not syncing after powerfail of server

Chris Albertson albertson.chris at gmail.com
Fri May 20 02:38:10 UTC 2011

On Thu, May 19, 2011 at 5:38 PM, Richard B. Gilbert
<rgilbert88 at comcast.net> wrote:
> On 5/19/2011 12:08 PM, M. Giertzsch wrote:
>> Am 19.05.2011 17:55, schrieb Chris Albertson:
>>> On Wed, May 18, 2011 at 2:57 AM, M. Giertzsch<mgiertzsch at mobotix.com>
>>> wrote:
>>>> Now if there is a powerfail, there is no guarantee that the server has
>>>> finished the boot
>>>> before the clients have. In this case the time will not be synced.
>>> If the clients are running the standard ntpd they will continue poling
>>> "forever" and the server can go up and down. The clients can sync to
>>> it when it is up and of course can't if it isn't.
>>> BTW it helps to have more than one NTP server. How do you know you
>>> server is serving correct time without some kind of redundant check?
>> Hi Chris,
>> thank you for your reply.
>> This is of course true, I can't say that that one server serves the
>> correct time.
>> But in a closed environment I can't guarantee that even when using more
>> servers.
>> If real time is needed I'm in need of a GPS module or something like this.
> A GPS Timing Receiver gives you time traceable to NIST.

If it is working and configured properly.  It is easy to have the time
"off" by a full second and there are examples of GPS driven NTP
servers that are far more than a second off.  You will never see that
kind of bug unless you have some kind of cross check set up.

Just for fun I set up and old Garmin nav GPS.  It was all over the
place, very poor time keeping realative to pool servers.

And I think "traceable" to NIST is the wrong term.  In this business
that word "traceable" has special meaning and some specific
administrative rules must be followed.   But in the general sense of
the word, outside of the way NIST uses it then yes the GPS times is
derived from a national standard.  --

Chris Albertson
Redondo Beach, California

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