ntp_gettime (3)
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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 argument, 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, maxerror, 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 adjtimex(2). Given a correct pointer argument, these functions always succeed.VERSIONS
The ntp_gettime() function is available since glibc 2.1. The ntp_gettimex() 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 TO
ntp_gettime() is described in the NTP Kernel Application Program Interface. ntp_gettimex() is a GNU extension.SEE ALSO
adjtimex(2) ntp_adjtime(3), time(7)NTP "Kernel Application Program Interface"