ntp_gettime(3)

NAME

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

LIBRARY

Standard C library (libc, -lc)

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.

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

STANDARDS

ntp_gettime(): NTP Kernel Application Program Interface.

ntp_gettimex(): GNU.

HISTORY

ntp_gettime(): glibc 2.1.

ntp_gettimex(): glibc 2.12.