[ntp:questions] Single best NTP status indicator of clock accuracy?

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Fri Jul 16 06:05:29 UTC 2010


kjans <kert.jans at gmail.com> writes:

> Hi,
>
>   I am looking for the best single indicator that can be used to
>   determine/monitor the current clock accuracy.

"Best and single" seem to contradict. What about "root dispersion"? ;-)

>
>   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 -clpeers)
>     - sync distance (from ntptrace)
>     - maximum error (from ntpdc)

estimated error, maybe.

>     - precision (from ntpq -crl)

That's a constant.

>     - ?
>
>   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
>
> # ntpq -crl
> assID=0 status=04f4 leap_none, sync_uhf_clock, 15 events, event_peer/
> strat_chg,
> version="ntpd 4.2.2p4 at 1.1585-o Fri Jun 15 10:17:41 UTC 2007 (1)",
> processor="i486", system="Linux/2.6.21-tinytgb5-pc", leap=00,
> stratum=1,
> precision=-16, rootdelay=0.000, rootdispersion=0.393, peer=56438,
> refid=MAL, reftime=cecbd50a.91b1b70c  Thu, Dec 10 2009 12:14:02.569,
> poll=10, clock=cecbd50f.302c13d6  Thu, Dec 10 2009 12:14:07.188,
> state=4, offset=0.057, frequency=-27.993, jitter=0.015, noise=0.015,
> stability=0.000, tai=0
>
>
> Thanks,
> Kert




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