1NTPSHMMON(1) GPSD Documentation NTPSHMMON(1)
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6 ntpshmmon - capture samples from gpsd or other ntpd refclock sources
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9 ntpshmmon [-?] [--count COUNT] [--help] [--offset] [--rmshm]
10 [--seconds SEC] [--verbose] [--version] [-h] [-n COUNT] [-o]
11 [-s] [-t SEC] [-v] [-V]
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14 This program monitors the shared-memory segments updated by gpsd(8) ,
15 and possibly other refclock sources, as a way of communicating with
16 ntpd, the Network Time Protocol daemon. It reads these in exactly the
17 way an ntpd instance does. It can be run concurrently with ntpd without
18 interfering with ntpd's normal operation.
19 This program runs forever, or until a termination option is matched, or
21 until interrupted, generating sample reports to standard output. Each
22 line consists of whitespace-separated textual fields.
23 Here is an example of the beginning of a report file:
25 ntpshmmon version 3.18
27 # Name Seen@ Clock Real L Pre
28 sample NTP2 1424926256.443030206 1424926256.115869233 1424926256.000000000 0 -1
29 sample NTP3 1424926256.443060517 1424926255.995430821 1424926256.000000000 0 -20
30 sample NTP3 1424926256.995747347 1424926256.995422728 1424926257.000000000 0 -20
31 sample NTP2 1424926257.112433572 1424926257.111936726 1424926257.000000000 0 -1
32 sample NTP3 1424926257.996221153 1424926257.995410232 1424926258.000000000 0 -20
33 sample NTP2 1424926258.107769409 1424926258.107451006 1424926258.000000000 0 -1
34 sample NTP3 1424926258.995647636 1424926258.995406476 1424926259.000000000 0 -20
35 The output always begins with a header line expressing the version of
37 the output format; the version line begins with "ntpshmmon version" and
38 is followed by a numeric version field.
39 The remainder of the file is either comments or sample lines. A comment
41 line begins with a # and should be ignored by programs that interpret
42 this format.
43 The fields of a sample line are as follows:
45 1. The keyword "sample"
47 2. The NTP unit from which it was collected.
49 3. Collection time of day, seconds.
51 4. Receiver time of day, seconds.
53 5. Clock time of day, seconds.
55 6. Leap-second notification status.
57 7. Source precision (log(2) of source jitter).
59 In these fields, "clock time" is the high-precision system clock time
61 measured by the source and "receiver time" is from the receiver. Both
62 times are in UTC. It is normal for the seconds part of receiver time to
63 coincide with the seconds part of collection time and for the
64 nanoseconds part of receiver time to be zero.
65 If the -o option is used, the "Seen@" column is replaced with the
67 "Offset" column. The "Offset" is the difference between "Clock" and
68 "Real" times.
69
71 -?, -h, --help
72 Display program usage and exit.
73 -n COUNT, --count COUNT
75 Set maximum number of samples to collect to COUNT.
76 -o, --offset
78 Replace the "Seen@" column with the "Offset" column. The "Offset"
79 is the difference between "Clock" and "Real" times.
80 -s, --rmshm
82 Remove all SHM segments used by GPSD. This option will normally
83 only be of interest to GPSD developers.
84 -t SECONDS, --seconds SECONDS
86 Set maximum time to collect samples in seconds to SECONDS.
87 -v, --verbose
89 Enable verbose status messages.
90 -V, --version
92 Display program version and exit.
93
95 gpsd(8), gpsdctl(8), gps(1), libgps(3), libgpsmm(3), gpsprof(1),
96 gpsfake(1).
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99 Eric S. Raymond <esr@thyrsus.com>.
100The GPSD Project 5 December 2020 NTPSHMMON(1)