[ntp:hackers] Single best indicator of clock accuracy?
Jans, Kert
kjans at solekai.com
Thu Dec 10 16:52:18 UTC 2009
Hi,
I am looking for the best single indicator that can be used to
determine/monitor the current clock accuracy.
I have several remote/embedded Linux devices that I am monitoring
via SNMP and want to monitor a single variable to know how accurate
the device thinks its time is.
There seems to be several possibilities:
- delay or offset or jitter (from ntpq)
- sync distance (from ntptrace)
- maximum error (from ntpdc)
- ?
Below is the output of several NTP status monitoring commands...
# ntpq -clpeers
remote refid st t when poll reach delay offset jitter
==============================================================================
LOCAL(0) .LOCL. 10 l 43 64 377 0.000 0.000 0.015
*GPS_NMEA(0) .MAL. 0 l 4 16 377 0.000 0.156 0.015
+ntp-2.gw.uiuc.e 128.118.25.5 2 u 41 64 377 71.652 2.432 0.528
+ntp-1.gw.uiuc.e 128.174.38.133 2 u 21 64 377 72.009 2.373 1.389
# ntptrace
localhost: stratum 1, offset 0.000159, synch distance 0.000539, refid 'MAL'
# ntpdc -c kerninfo 127.0.0.1
pll offset: 0.000151 s
pll frequency: -27.934 ppm
maximum error: 0.007856 s
estimated error: 1.5e-05 s
status: 0001 pll
pll time constant: 4
precision: 1e-06 s
frequency tolerance: 512 ppm
Thanks,
Kert
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