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.
GNU.

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