man3/ntp_gettime.3

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  25 .TH NTP_GETTIME 3 2017-09-15 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 ntp_gettime, ntp_gettimex  \- get time parameters (NTP daemon interface)
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <sys/timex.h>
  31 .PP
  32 .BI "int ntp_gettime(struct ntptimeval *" ntv );
  33 .PP
  34 .BI "int ntp_gettimex(struct ntptimeval *" ntv );
  35 .fi
  36 .SH DESCRIPTION
  37 Both of these APIs return information to the caller via the
  38 .I ntv
  39 argument, a structure of the following type:
  40 .PP
  41 .in +4n
  42 .EX
  43 struct ntptimeval {
  44     struct timeval time;        /* Current time */
  45     long int maxerror;          /* Maximum error */
  46     long int esterror;          /* Estimated error */
  47     long int tai;               /* TAI offset */
  48
  49     /* Further padding bytes allowing for future expansion */
  50 };
  51 .EE
  52 .in
  53 .PP
  54 The fields of this structure are as follows:
  55 .TP
  56 .I time
  57 The current time, expressed as a
  58 .I timeval
  59 structure:
  60 .IP
  61 .in +4n
  62 .EX
  63 struct timeval {
  64     time_t      tv_sec;   /* Seconds since the Epoch */
  65     suseconds_t tv_usec;  /* Microseconds */
  66 };
  67 .EE
  68 .in
  69 .IP
  70 .TP
  71 .I maxerror
  72 Maximum error, in microseconds.
  73 This value can be initialized by
  74 .BR ntp_adjtime (3),
  75 and is increased periodically (on Linux: each second),
  76 but is clamped to an upper limit (the kernel constant
  77 .BR NTP_PHASE_MAX ,
  78 with a value of 16,000).
  79 .TP
  80 .I esterror
  81 Estimated error, in microseconds.
  82 This value can be set via
  83 .BR ntp_adjtime (3)
  84 to contain an estimate of the difference between the system clock
  85 and the true time.
  86 This value is not used inside the kernel.
  87 .TP
  88 .I tai
  89 TAI (Atomic International Time) offset.
  90 .PP
  91 .BR ntp_gettime ()
  92 returns an
  93 .I ntptimeval
  94 structure in which the
  95 .IR time ,
  96 .IR maxerror ,
  97 and
  98 .IR esterror
  99 fields are filled in.
 100 .PP
 101 .BR ntp_gettimex ()
 102 performs the same task as
 103 .BR ntp_gettime (),
 104 but also returns information in the
 105 .I tai
 106 field.
 107 .SH RETURN VALUE
 108 The return values for
 109 .BR ntp_gettime ()
 110 and
 111 .BR ntp_gettimex ()
 112 are as for
 113 .BR adjtimex (2).
 114 Given a correct pointer argument, these functions always succeed.
 115 .\" FIXME . the info page incorrectly describes the return values.
 116 .SH VERSIONS
 117 The
 118 .BR ntp_gettime ()
 119 function is available since glibc 2.1.
 120 The
 121 .BR ntp_gettimex ()
 122 function is available since glibc 2.12.
 123 .SH ATTRIBUTES
 124 For an explanation of the terms used in this section, see
 125 .BR attributes (7).
 126 .TS
 127 allbox;
 128 lbw30 lb lb
 129 l l l.
 130 Interface       Attribute       Value
 131 T{
 132 .BR ntp_gettime (),
 133 .BR ntp_gettimex ()
 134 T}      Thread safety   MT-Safe
 135 .TE
 136 .SH CONFORMING TO
 137 .BR ntp_gettime ()
 138 is described in the NTP Kernel Application Program Interface.
 139 .BR ntp_gettimex ()
 140 is a GNU extension.
 141 .SH SEE ALSO
 142 .BR adjtimex (2)
 143 .BR ntp_adjtime (3),
 144 .BR time (7)
 145 .PP
 146 .ad l
 147 .UR http://www.slac.stanford.edu/comp/unix/\:package/\:rtems/\:src/\:ssrlApps/\:ntpNanoclock/\:api.htm
 148 NTP "Kernel Application Program Interface"
 149 .UE