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NTPSHMMON(1)		      GPSD Documentation		  NTPSHMMON(1)

       ntpshmmon - capture samples from	gpsd or	other ntpd refclock sources

       ntpshmmon [-?] [-h] [-n nsamples] [-o] [-s] [-t nseconds] [-v] [-V]

       This program monitors the shared-memory segments	updated	by gpsd(8) ,
       and possibly other refclock sources, as a way of	communicating with
       ntpd, the Network Time Protocol daemon. It reads	these in exactly the
       way an ntpd instance does. It can be run	concurrently with ntpd without
       interfering with	ntpd's normal operation.

       This program runs forever, or until a termination option	is matched, or
       until interrupted, generating sample reports to standard	output.	Each
       line consists of	whitespace-separated textual fields.

       Here is an example of the beginning of a	report file:

	   ntpshmmon version 3.18
	   #	  Name	 Seen@		      Clock		   Real		      L	Pre
	   sample NTP2 1424926256.443030206 1424926256.115869233 1424926256.000000000 0	 -1
	   sample NTP3 1424926256.443060517 1424926255.995430821 1424926256.000000000 0	-20
	   sample NTP3 1424926256.995747347 1424926256.995422728 1424926257.000000000 0	-20
	   sample NTP2 1424926257.112433572 1424926257.111936726 1424926257.000000000 0	 -1
	   sample NTP3 1424926257.996221153 1424926257.995410232 1424926258.000000000 0	-20
	   sample NTP2 1424926258.107769409 1424926258.107451006 1424926258.000000000 0	 -1
	   sample NTP3 1424926258.995647636 1424926258.995406476 1424926259.000000000 0	-20

       The output always begins	with a header line expressing the version of
       the output format; the version line begins with "ntpshmmon version" and
       is followed by a	numeric	version	field.

       The remainder of	the file is either commments or	sample lines. A
       comment line begins with	a # and	should ignored by programs that
       interpret this format.

       The fields of a sample line are as follows:

	1. The keyword "sample"

	2. The NTP unit	from which it was collected.

	3. Collection time of day, seconds.

	4. Receiver time of day, seconds.

	5. Clock time of day, seconds.

	6. Leap-second notification status.

	7. Source precision (log(2) of source jitter).

       In these	fields,	"clock time" is	the high-precision system clock	time
       measured	by the source and "receiver time" is from the receiver.	Both
       times are in UTC. It is normal for the seconds part of receiver time to
       coincide	with the seconds part of collection time and for the
       nanoseconds part	of receiver time to be zero.

       If the -o option	is used, the "Seen@" column is replaced	with the
       "Offset"	column.	The "Offset" is	the difference between "Clock" and
       "Real" times.

	   Display program usage and exit.

	   Display program usage and exit.

	   Set maximum number of samples to collect.

	   Replace the "Seen@" column with the "Offset"	column.	The "Offset"
	   is the difference between "Clock" and "Real"	times.

	   Remove all SHM segments used	by GPSD. This option will normally
	   only	be of interest to GPSD developers.

	   Set maximum time to collect samples in seconds.

	   Enable verbose status messages.

	   Display program version and exit.

       gpsd(8),	gpsdctl(8), gps(1), libgps(3), libgpsmm(3), gpsprof(1),

       Eric S. Raymond <>.

The GPSD Project		  21 Dec 2018			  NTPSHMMON(1)


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