ntp_gettime (3)

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Copyright (c) 2016 by Michael Kerrisk <mtk.manpages@gmail.com>

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(The comments found at the beginning of the groff file "man3/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 int maxerror;          /* Maximum error */
    long int esterror;          /* Estimated error */
    long int 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"

COLOPHON

This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at www.kernel.org/doc/man-pages