SNTP from Python: getting server's esimate of time quality

Anders Wallin recently discussed generating graphs of server time error using a timestamp from the Date: header of an http request.

NTP servers themselves have estimates of time error, and it's possible to get the local server's idea of the error by sending SNTP packets to the local machine. You can also see the last time this NTP server successfully communicated with a peer or upstream, and see whether the server considers itself desynchronized by checking the stratum and leap second fields.

Based on my tinkering, the root_dispersion field or the derived LAMBDA value is the easiest to look at for estimating how bad the NTP time is. Between communications with a peer, root_dispersion and LAMBA increase at a rate of 15µs/s, ntp's arbitrary estimate of the accuracy of the local undisciplined clock. (YMMV and you can appaerntly tweak CLOCK_PHI in your NTP configuration file)

The attached program is a basic Python SNTP client which by default polls the local server every 5 seconds and prints some information. License: GPLv2+

Typical output:

12:25:58  0.06233  228.95875 ST-SYNCH LI-SYNCH
12:26:03  0.06241  233.96404 ST-SYNCH LI-SYNCH
12:26:08  0.06247  238.96745 ST-SYNCH LI-SYNCH
12:26:13  0.06255  243.97141 ST-SYNCH LI-SYNCH
12:26:18  0.06262  248.97673 ST-SYNCH LI-SYNCH
12:26:23  0.06270  253.98213 ST-SYNCH LI-SYNCH
12:26:28  0.06277  258.98746 ST-SYNCH LI-SYNCH

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Entry first conceived on 23 November 2013, 18:19 UTC, last modified on 27 January 2014, 18:03 UTC
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