Linux man pages

Section (3) ntp_gettime

Linux manual pages	Section 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.

COLOPHON

This page is part of release 4.16 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 https://www.kernel.org/doc/man−pages/.

  Copyright (c) 2016 by Michael Kerrisk <mtk.manpagesgmail.com>

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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 */
};

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