1NTPSHMMON(1) GPSD Documentation NTPSHMMON(1)
2
6 ntpshmmon - capture samples from gpsd or other ntpd refclock sources
7
9 ntpshmmon [OPTIONS]
10 ntpshmmon -h
12 ntpshmmon -V
14
16 This program monitors the shared-memory segments updated by gpsd 8 ,
17 and possibly other refclock sources, as a way of communicating with
18 ntpd, the Network Time Protocol daemon. It reads these in exactly the
19 way an ntpd instance does. It can be run concurrently with ntpd without
20 interfering with ntpd’s normal operation.
21 ntpshmmon requires root privileges to access the root only NTP0 and
23 NTP1. Running as a normal user will only allow access to NTP2 and NTP3.
24 cause loss of functionality.
25 This program runs forever, or until a termination option is matched, or
27 until interrupted, generating sample reports to standard output. Each
28 line consists of whitespace-separated textual fields.
29 Here is an example of the beginning of a report file:
31 ntpshmmon version 3.18
33 # Name Seen@ Clock Real L Pre
34 sample NTP2 1424926256.443030206 1424926256.115869233 1424926256.000000000 0 -1
35 sample NTP3 1424926256.443060517 1424926255.995430821 1424926256.000000000 0 -20
36 sample NTP3 1424926256.995747347 1424926256.995422728 1424926257.000000000 0 -20
37 sample NTP2 1424926257.112433572 1424926257.111936726 1424926257.000000000 0 -1
38 sample NTP3 1424926257.996221153 1424926257.995410232 1424926258.000000000 0 -20
39 sample NTP2 1424926258.107769409 1424926258.107451006 1424926258.000000000 0 -1
40 sample NTP3 1424926258.995647636 1424926258.995406476 1424926259.000000000 0 -20
41 The output always begins with a header line expressing the version of
43 the output format; the version line begins with "ntpshmmon version" and
44 is followed by a numeric version field.
45 The remainder of the file is either comments or sample lines. A comment
47 line begins with a # and should be ignored by programs that interpret
48 this format.
49 The fields of a sample line are as follows:
51 1. The keyword "sample"
53 2. The NTP unit from which it was collected.
55 3. Collection time of day, seconds.
57 4. Receiver time of day, seconds.
59 5. Clock time of day, seconds.
61 6. Leap-second notification status.
63 7. Source precision (log(2) of source jitter).
65 In these fields, "clock time" is the high-precision system clock time
67 measured by the source and "receiver time" is from the receiver. Both
68 times are in UTC. It is normal for the seconds part of receiver time to
69 coincide with the seconds part of collection time and for the
70 nanoseconds part of receiver time to be zero.
71 If the -o option is used, the "Seen@" column is replaced with the
73 "Offset" column. The "Offset" is the difference between "Clock" and
74 "Real" times.
75
77 -?, -h, --help
78 Display program usage and exit.
79 -n COUNT, --count COUNT
81 Set maximum number of samples to collect to COUNT.
82 -o, --offset
84 Replace the "Seen@" column with the "Offset" column. The "Offset"
85 is the difference between "Clock" and "Real" times.
86 -s, --rmshm
88 Remove all SHM segments used by GPSD. This option will normally
89 only be of interest to GPSD developers.
90 -t SECONDS, --seconds SECONDS
92 Set maximum time to collect samples in seconds to SECONDS.
93 -v, --verbose
95 Enable verbose status messages.
96 -V, --version
98 Display program version and exit.
99
101 0
102 on success.
103 1
105 on failure
106
108 gpsd(8), gps(1)
109
111 Project web site: https://gpsd.io/
112
114 This file is Copyright 2013 by the GPSD project
115 SPDX-License-Identifier: BSD-2-clause
116
118 Eric S. Raymond
119GPSD, Version 3.24 2021-09-20 NTPSHMMON(1)