[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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