man3/ntp_gettime.3

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.TH NTP_GETTIME 3 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
ntp_gettime, ntp_gettimex  \- get time parameters (NTP daemon interface)
.SH SYNOPSIS
.nf
.B #include <sys/timex.h>
.PP
.BI "int ntp_gettime(struct ntptimeval *" ntv );
.PP
.BI "int ntp_gettimex(struct ntptimeval *" ntv );
.fi
.SH DESCRIPTION
Both of these APIs return information to the caller via the
.I ntv
argument, a structure of the following type:
.PP
.in +4n
.EX
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 */
};
.EE
.in
.PP
The fields of this structure are as follows:
.TP
.I time
The current time, expressed as a
.I timeval
structure:
.IP
.in +4n
.EX
struct timeval {
    time_t      tv_sec;   /* Seconds since the Epoch */
    suseconds_t tv_usec;  /* Microseconds */
};
.EE
.in
.IP
.TP
.I maxerror
Maximum error, in microseconds.
This value can be initialized by
.BR ntp_adjtime (3),
and is increased periodically (on Linux: each second),
but is clamped to an upper limit (the kernel constant
.BR NTP_PHASE_MAX ,
with a value of 16,000).
.TP
.I esterror
Estimated error, in microseconds.
This value can be set via
.BR 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.
.TP
.I tai
TAI (Atomic International Time) offset.
.PP
.BR ntp_gettime ()
returns an
.I ntptimeval
structure in which the
.IR time ,
.IR maxerror ,
and
.IR esterror
fields are filled in.
.PP
.BR ntp_gettimex ()
performs the same task as
.BR ntp_gettime (),
but also returns information in the
.I tai
field.
.SH RETURN VALUE
The return values for
.BR ntp_gettime ()
and
.BR ntp_gettimex ()
are as for
.BR adjtimex (2).
Given a correct pointer argument, these functions always succeed.
.\" FIXME . the info page incorrectly describes the return values.
.SH VERSIONS
The
.BR ntp_gettime ()
function is available since glibc 2.1.
The
.BR ntp_gettimex ()
function is available since glibc 2.12.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw30 lb lb
l l l.
Interface	Attribute	Value
T{
.BR ntp_gettime (),
.BR ntp_gettimex ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
.BR ntp_gettime ()
is described in the NTP Kernel Application Program Interface.
.BR ntp_gettimex ()
is a GNU extension.
.SH SEE ALSO
.BR adjtimex (2)
.BR ntp_adjtime (3),
.BR time (7)
.PP
.ad l
.UR http://www.slac.stanford.edu/comp/unix/\:package/\:rtems/\:src/\:ssrlApps/\:ntpNanoclock/\:api.htm
NTP "Kernel Application Program Interface"
.UE