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NTP_GETTIME(3)                                                          Linux Programmer's Manual                                                         NTP_GETTIME(3)

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

SYNOPSIS
       #include <sys/timex.h>

       int ntp_gettime(struct ntptimeval *ntv);
       int ntp_gettimex(struct ntptimeval *ntv);

DESCRIPTION
       Both of these APIs return information to the caller via the ntv argument, a structure of the following type:

           struct ntptimeval {
               struct timeval time;    /* Current time */
               long maxerror;          /* Maximum error */
               long esterror;          /* Estimated error */
               long tai;               /* TAI offset */

               /* Further padding bytes allowing for future expansion */
           };

       The fields of this structure are as follows:

       time   The current time, expressed as a timeval structure:

                  struct timeval {
                      time_t      tv_sec;   /* Seconds since the Epoch */
                      suseconds_t tv_usec;  /* Microseconds */
                  };

       maxerror
              Maximum error, in microseconds.  This value can be initialized by ntp_adjtime(3), and is increased periodically (on Linux: each second), but is clamped to
              an upper limit (the kernel constant NTP_PHASE_MAX, with a value of 16,000).

       esterror
              Estimated error, in microseconds.  This value can be set via ntp_adjtime(3) to contain an estimate of the difference between the system clock and the true
              time.  This value is not used inside the kernel.

       tai    TAI (Atomic International Time) offset.

       ntp_gettime() returns an ntptimeval structure in which the time, maxerror, and esterror fields are filled in.

       ntp_gettimex() performs the same task as ntp_gettime(), but also returns information in the tai field.

RETURN VALUE
       The return values for ntp_gettime() and ntp_gettimex() are as for adjtimex(2).  Given a correct pointer argument, these functions always succeed.

VERSIONS
       The ntp_gettime() function is available since glibc 2.1.  The ntp_gettimex() function is available since glibc 2.12.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                                                                                             │ Attribute     │ Value   │
       ├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ntp_gettime(), ntp_gettimex()                                                                                                         │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO
       ntp_gettime() is described in the NTP Kernel Application Program Interface.  ntp_gettimex() is a GNU extension.

SEE ALSO
       adjtimex(2), ntp_adjtime(3), time(7)

       NTP "Kernel Application Program Interface" ⟨http://www.slac.stanford.edu/comp/unix/package/rtems/src/ssrlApps/ntpNanoclock/api.htm⟩

Linux                                                                          2021-03-22                                                                 NTP_GETTIME(3)