[ntp:questions] Output of ntpq -p regarding stratum level

Unruh unruh-spam at physics.ubc.ca
Wed Sep 10 22:49:06 UTC 2008


Stefan.Nottorf at plath.de (Nottorf, Stefan) writes:

>Hello,
>although this is probably a beginner's question, I would like to
>understand this before I run into trouble caused by misunderstanding
>basic information. I think i misunderstood how to read the output of
>ntpq -p... 
>The third column ("st") shows the stratum.
>But beginning to monitor time synchronization in our network, I noticed
>a slight difference in the understanding of stratum levels between me
>and the monitoring tool (Nagios).
>When I use ntpq -p on one of our hosts I get the following output:

>remote      refid   st t when poll reach delay offset   jitter
>========================================================================
>======
>*10.x.y.z   .PPS.    1 u  338 1024  377  0.454 -1.559   0.078
>name1.name  10.x.y.z 2 u  471 1024  376  0.209  1.763   0.093
>name2.name  10.x.y.z 2 u 1461 1024  374  0.001  2.652   0.206
>name3.name  10.x.y.z 2 u  596 1024  376  0.385  0.052   0.322
>LOCAL(0)    .LOCL.   5 l   59   64  377  0.000  0.000   0.001

>Until now I read this line :*10.x.y.z   .PPS.    1 u  338 1024  377
>0.454 -1.559   0.078
>the following way:
>The host I ran ntpq -p on is synchronized to (*) server 10.x.y.z., whose
>time source is a PulsePerSecond clock. 10.x.y.z is a server at stratum 1
>and 338 seconds have passed since the last poll. The poll interval is
>1024 seconds.

The PPS clock is stratum 0. The host synced to that is stratum 1. The host
synced to a stratum 1 is stratum 2, etc.

>Because the time reference is located at stratum 1, this host is located
>at stratum 2.
>Similarily, if I look at server name1.name: name1.name is a server
>located at stratum 2 and is itself synchronized to server 10.x.y.z.
>If this is correct so far, the following output confuses me. I ran a
>check for time synchronization for Nagios. Nagios provides a couple of
>checks, one of them called check_ntp_peer. I use it to detect
>differences between expected and current stratum levels.

>/<installation_path>/libexec/check_ntp_peer -H name1.name -W 4 -C 6 -v

>1 candiate peers available
>synchronization source found
>Getting offset, jitter and stratum for peer 4551
>parsing offset from peer 4551: -0.001193
>parsing stratum from peer 4551: 1
>NTP OK: Offset -0.001193 secs,
>stratum=1|offset=-0.001193s;60.000000;120.000000; stratum=1;4;6;0;16

>This output tells me, that name1.name is located in stratum 1 (instead
>of the expected stratum 2). 

This is an issue with nagios. 



>In short: does the column st refer to the stratum of the remote host OR
>does it mean "If I synchronize to that remote host I will get to stratum
>x" ?

As you can see, the machine that is synced to the pps is stratum 1 .

>Thanks and regards,
>Stefan Nottorf




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