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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:

The current time, expressed as a timeval structure:

struct timeval {

time_t tv_sec; /* Seconds since the Epoch */
suseconds_t tv_usec; /* Microseconds */ };

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).
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 (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 Kernel Application Program Interface.


glibc 2.1.
glibc 2.12.


adjtimex(2), ntp_adjtime(3), time(7)

NTP "Kernel Application Program Interface"

2024-05-02 Linux man-pages 6.8