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 argu‐
ment, 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, maxer‐
ror, 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 adj‐
timex(2). Given a correct pointer argument, these functions always
succeed.
VERSIONS
The ntp_gettime() function is available since glibc 2.1. The ntp_get‐
timex() 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 TOntp_gettime() is described in the NTP Kernel Application Program Inter‐
face. ntp_gettimex() is a GNU extension.
SEE ALSOadjtimex(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⟩
COLOPHON
This page is part of release 4.14 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/.
Linux 2017-09-15 NTP_GETTIME(3)
