ntp_gettime(3)

1ntp_gettime(3)             Library Functions Manual             ntp_gettime(3)
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NAME

6       ntp_gettime, ntp_gettimex  - get time parameters (NTP daemon interface)
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <sys/timex.h>
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14       int ntp_gettime(struct ntptimeval *ntv);
15       int ntp_gettimex(struct ntptimeval *ntv);
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DESCRIPTION

18       Both  of  these APIs return information to the caller via the ntv argu‐
19       ment, a structure of the following type:
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21           struct ntptimeval {
22               struct timeval time;    /* Current time */
23               long maxerror;          /* Maximum error */
24               long esterror;          /* Estimated error */
25               long tai;               /* TAI offset */
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27               /* Further padding bytes allowing for future expansion */
28           };
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30       The fields of this structure are as follows:
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32       time   The current time, expressed as a timeval structure:
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34                  struct timeval {
35                      time_t      tv_sec;   /* Seconds since the Epoch */
36                      suseconds_t tv_usec;  /* Microseconds */
37                  };
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39       maxerror
40              Maximum error, in microseconds.  This value can  be  initialized
41              by ntp_adjtime(3), and is increased periodically (on Linux: each
42              second), but is clamped to an upper limit (the  kernel  constant
43              NTP_PHASE_MAX, with a value of 16,000).
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45       esterror
46              Estimated  error,  in  microseconds.   This value can be set via
47              ntp_adjtime(3) to contain an estimate of the difference  between
48              the  system clock and the true time.  This value is not used in‐
49              side the kernel.
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51       tai    TAI (Atomic International Time) offset.
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53       ntp_gettime() returns an ntptimeval structure in which the time, maxer‐
54       ror, and esterror fields are filled in.
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56       ntp_gettimex()  performs  the  same task as ntp_gettime(), but also re‐
57       turns information in the tai field.
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RETURN VALUE

60       The return values for ntp_gettime() and ntp_gettimex() are as for  adj‐
61       timex(2).   Given  a  correct  pointer argument, these functions always
62       succeed.
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ATTRIBUTES

65       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
66       tributes(7).
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68       ┌────────────────────────────────────────────┬───────────────┬─────────┐
69       │Interface                                   │ Attribute     │ Value   │
70       ├────────────────────────────────────────────┼───────────────┼─────────┤
71       │ntp_gettime(), ntp_gettimex()               │ Thread safety │ MT-Safe │
72       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

75       ntp_gettime()
76              NTP Kernel Application Program Interface.
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78       ntp_gettimex()
79              GNU.
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HISTORY

82       ntp_gettime()
83              glibc 2.1.
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85       ntp_gettimex()
86              glibc 2.12.
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