[ntp:questions] Unable to use SUSE Linux for time synchronization.

Richard B. gilbert rgilbert88 at comcast.net
Fri Feb 9 20:28:55 UTC 2007

sandy wrote:
> Hi,
> I am trying to use Linux NTP server for time sync with my target in
> unicast mode. This target has the sntp client version 4 as per RFC
> 2030. I tried to time sync using windows domain controller. With
> windows DC as time server, it works fine.
> I have problem when using SUSE Linux as time server. When I try to use
> linux as time server, Linux replies with LI leap indicator flags set
> to "alarm condition (clock not synchronized)". As per RFC 2030, as
> unicast mode is used, as LI is 3, the reply is getting rejected. My
> Linux time server is standalone system. It is not getting time synched
> with external source. Could this the be the reason ?
It is almost certainly the reason!

> I tried to use the Linux time server as client. But even in this case
> too, Linux request has the
> Leap indicator value set to 3.
> Can you please tell me what could be wrong  ? What exactly is meant by
> ""alarm condition (clock not synchronized)" ?  How to make use of
> Linux NTP server correctly ?
> Is it related to configuration issue ? Do I need to use a particular
> stratum ?

It is a common misconception that NTP is supposed to synchronize 
computer clocks to each other!

NTP was designed to synchronize computer clocks to UTC!  In order to use 
NTP properly you need a time source traceable to UTC.  The 
synchronization of clocks to each other is a happy consequence of the 
postulate "things equal to the same thing are equal to each other"!

You may use a "hardware reference clock"; e.g. a GPS timing receiver, a 
WWV/WWVH receiver, a LORAN receiver, or an "atomic clock" which DOES NOT 
mean the radio controlled clocks you can buy for $10-$50.

You may also use internet NTP servers which have time traceable to UTC. 
  There is a list of such servers at 

Unless you are serving time to 100 or more clients, you should pick 
servers from the "Stratum 2" list.

If you cannot access the internet for this purpose, you can buy a Garmin 
GPS18-LVC timing receiver for less than $100 US.  You connect it to a 
serial port on your time server, some soldering required (you have to 
solder a DB9 connector to the cable).  You also need to provide a 5VDC 
power supply.  This should synchronize your server's clock to within a 
few microseconds.  GPS is a superbly stable and accurate reference and 
your server's clients, on your LAN, should be able to synchronize 
tightly with it; e.g. within a few tens of microseconds.

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