bsd/man/man2/adjtime.2

   1 .\"     $NetBSD: adjtime.2,v 1.5 1995/10/12 15:40:44 jtc Exp $
   2 .\"
   3 .\" Copyright (c) 1980, 1991, 1993
   4 .\"     The Regents of the University of California.  All rights reserved.
   5 .\"
   6 .\" Redistribution and use in source and binary forms, with or without
   7 .\" modification, are permitted provided that the following conditions
   8 .\" are met:
   9 .\" 1. Redistributions of source code must retain the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer.
  11 .\" 2. Redistributions in binary form must reproduce the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer in the
  13 .\"    documentation and/or other materials provided with the distribution.
  14 .\" 3. All advertising materials mentioning features or use of this software
  15 .\"    must display the following acknowledgement:
  16 .\"     This product includes software developed by the University of
  17 .\"     California, Berkeley and its contributors.
  18 .\" 4. Neither the name of the University nor the names of its contributors
  19 .\"    may be used to endorse or promote products derived from this software
  20 .\"    without specific prior written permission.
  21 .\"
  22 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32 .\" SUCH DAMAGE.
  33 .\"
  34 .\"     @(#)adjtime.2   8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt ADJTIME 2
  38 .Os BSD 4.3
  39 .Sh NAME
  40 .Nm adjtime
  41 .Nd "correct the time to allow synchronization of the system clock"
  42 .Sh SYNOPSIS
  43 .Fd #include <sys/time.h>
  44 .Ft int
  45 .Fn adjtime "const struct timeval *delta" "struct timeval *olddelta"
  46 .Sh DESCRIPTION
  47 .Fn Adjtime
  48 makes small adjustments to the system time, as returned by
  49 .Xr gettimeofday 2 ,
  50 advancing or retarding it
  51 by the time specified by the timeval
  52 .Fa delta .
  53 If
  54 .Fa delta
  55 is negative, the clock is
  56 slowed down by incrementing it more slowly than normal until
  57 the correction is complete.
  58 If
  59 .Fa delta
  60 is positive, a larger increment than normal
  61 is used.
  62 The skew used to perform the correction is generally a fraction of one percent.
  63 Thus, the time is always
  64 a monotonically increasing function.
  65 A time correction from an earlier call to
  66 .Fn adjtime
  67 may not be finished when
  68 .Fn adjtime
  69 is called again.
  70 If
  71 .Fa olddelta
  72 is non-nil,
  73 the structure pointed to will contain, upon return, the
  74 number of microseconds still to be corrected
  75 from the earlier call.
  76 .Pp
  77 This call may be used by time servers that synchronize the clocks
  78 of computers in a local area network.
  79 Such time servers would slow down the clocks of some machines
  80 and speed up the clocks of others to bring them to the average network time.
  81 .Pp
  82 The call
  83 .Fn adjtime
  84 is restricted to the super-user.
  85 .Sh RETURN VALUES
  86 A return value of 0 indicates that the call succeeded.
  87 A return value of -1 indicates that an error occurred, and in this
  88 case an error code is stored in the global variable
  89 .Va errno .
  90 .Sh ERRORS
  91 .Fn Adjtime
  92 will fail if:
  93 .Bl -tag -width Er
  94 .It Bq Er EFAULT
  95 An argument points outside the process's allocated address space.
  96 .It Bq Er EPERM
  97 The process's effective user ID is not that of the super-user.
  98 .El
  99 .Sh SEE ALSO
 100 .Xr date 1 ,
 101 .Xr gettimeofday 2 ,
 102 .Xr timed 8 ,
 103 .Xr timedc 8
 104 .Rs
 105 .%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
 106 .%A R. Gusella
 107 .%A S. Zatti
 108 .Re
 109 .Sh HISTORY
 110 The
 111 .Fn adjtime
 112 function call appeared in
 113 .Bx 4.3 .