[ntp:questions] Re: OpenNTP on PCBSD

Richard B. Gilbert rgilbert88 at comcast.net
Thu Dec 22 21:37:55 UTC 2005


MikeT wrote:

>I am new to *nix, so bear with me.. I have installed OpenNTP 3.7 on
>PCBSD 5.4 w/KDE 3.4.  I have configured the rc.conf and the ntpd.conf
>properly (I think) and rebooted.  I am going to connect this directly
>to a Trimble satellite time-synch device.  How do I tell if it is
>properly synched?  Is there a command or something I can run through
>KDE to check this? 
>
>Any help is appreciated!
>
>Mike
>
>  
>
OpenNTP is rather a sore point around here.   The last time I heard, it 
was not compliant with either the NTP v3 RFC or the draft spec for NTP 
v4.   Use at your own risk.

There is a reference implementation of ntpd v4.2 and accessories 
available at
http://ntp.isc.org/bin/view/Main/SoftwareDownloads
The reference implementation is the result of something like twenty 
years of research, development and testing.  It's a tough act to follow.

You can build it yourself if you have gcc.

The following applies to the reference implementation.

The nptq -p command should produce a display showing

Remote      REFID      Stratum   Type When   Reach   Delay   Offset   Jitter

Where "Remote" gives the IP address of the server or the pseudo address 
of the hardware reference clock if you are using one, REFID identifies 
the source of the time supplied by "Remote", "Stratum" gives the stratum 
of the server, "Type" the type of the server, "When" when it last 
responded to a poll,
"Reach" is an eight bit shift register with bits shifted in from the 
right; a one bit indicates a reply a zero no reply 377 is good and 0 is 
not, Delay  is the round trip delay in getting a packet to and from the 
server, offset is the difference between the server's clock and yours, 
and and "Jitter" is a measure of the random noise in the time supplied 
by the server.

The ntpq -p display is most useful after several minutes have elapsed 
since ntpd started.  Ntpd needs five replies from a server before it 
will consider using it for synchronization.   If you do not use the 
"iburst" qualifier in your server statement in ntp.conf, it will take 
approximately 320 seconds to get the first five replies from each 
server.   If you use "iburst" it should take only eighty seconds to get 
the first five replies.

The first character in the line may be "*" indicating the server has 
been selected for synchronization,  "+" indicating the the server is 
acting as part of an  advisory committee, "-" indicating the the server 
is not being used, or "x" meaning that the server is considered "insane",

Offset and delay are in milliseconds.  Low numbers are good and high 
bad.   I look for delay to be less than thirty milliseconds for an 
internet server or less than one millisecond for a LAN server..  Offset 
should be less than ten milliseconds for an internet server that you are 
synchronized with.  If you have a hardware reference clock, the offset 
should be down in the low microseconds for a GPS based reference clock




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