123 lines
4 KiB
Groff
123 lines
4 KiB
Groff
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.\" $NetBSD: adjtime.2,v 1.20 2004/05/13 10:20:57 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd June 4, 1993
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.Dt ADJTIME 2
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.Os
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.Sh NAME
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.Nm adjtime
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.Nd "correct the time to allow synchronization of the system clock"
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/time.h
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.Ft int
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.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta"
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.Sh DESCRIPTION
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.Fn adjtime
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makes small adjustments to the system time, as returned by
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.Xr gettimeofday 2 ,
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advancing or retarding it
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by the time specified by the timeval
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.Fa delta .
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If
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.Fa delta
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is negative, the clock is
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slowed down by incrementing it more slowly than normal until
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the correction is complete.
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If
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.Fa delta
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is positive, a larger increment than normal
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is used.
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The skew used to perform the correction is generally a fraction of one percent.
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Thus, the time is always
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a monotonically increasing function.
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A time correction from an earlier call to
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.Fn adjtime
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may not be finished when
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.Fn adjtime
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is called again.
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If
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.Fa olddelta
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is non-nil,
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the structure pointed to will contain, upon return, the
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number of microseconds still to be corrected
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from the earlier call.
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.Pp
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This call may be used by time servers that synchronize the clocks
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of computers in a local area network.
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Such time servers would slow down the clocks of some machines
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and speed up the clocks of others to bring them to the average network time.
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.Pp
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If the calling user is not the super user, then the
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.Fn adjtime
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function in the standard C library will try to use the
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.Xr clockctl 4
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device if present, thus making possible for non privileged users to
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adjust the system time.
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If
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.Xr clockctl 4
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is not present or not accessible, then
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.Fn adjtime
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reverts to the
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.Fn adjtime
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system call, which is restricted to the super user.
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.Sh RETURN VALUES
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A return value of 0 indicates that the call succeeded.
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A return value of \-1 indicates that an error occurred, and in this
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case an error code is stored in the global variable
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.Va errno .
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.Sh ERRORS
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.Fn adjtime
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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An argument points outside the process's allocated address space.
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.It Bq Er EPERM
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The process's effective user ID is not that of the super user.
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.El
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.Sh SEE ALSO
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.Xr date 1 ,
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.Xr gettimeofday 2 ,
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.Xr clockctl 4 ,
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.Xr timed 8 ,
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.Xr timedc 8
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.Rs
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.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
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.%A R. Gusella
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.%A S. Zatti
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.Re
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.Sh HISTORY
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The
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.Fn adjtime
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function call appeared in
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.Bx 4.3 .
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