ntp_gettime(3) Library Functions Manual 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 argu-
ment, 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 in-
side 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 re-
turns 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 at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ntp_gettime(), ntp_gettimex() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
ntp_gettime() is described in the NTP Kernel Application Program Inter-
face. ntp_gettimex() is a GNU extension.
SEE ALSO
adjtimex(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⟩
Linux man-pages 6.03 2022-12-15 ntp_gettime(3)
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