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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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ntp_gettime(3) Library Functions Manual ntp_gettime(3)
ntp_gettime, ntp_gettimex - get time parameters (NTP daemon
interface)
Standard C library (libc, -lc)
#include <sys/timex.h>
int ntp_gettime(struct ntptimeval *ntv);
int ntp_gettimex(struct ntptimeval *ntv);
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.
The return values for ntp_gettime() and ntp_gettimex() are as for
adjtimex(2). Given a correct pointer argument, these functions
always succeed.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ ntp_gettime(), ntp_gettimex() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
ntp_gettime()
NTP Kernel Application Program Interface.
ntp_gettimex()
GNU.
ntp_gettime()
glibc 2.1.
ntp_gettimex()
glibc 2.12.
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⟩
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 ntp_gettime(3)
Pages that refer to this page: adjtimex(2), time(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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