NTP_GETTIME

Section: Linux Programmer's Manual (3)
Updated: 2020-11-01
Page Index

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.

COLOPHON

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