1997-05-12 12:13:10 +00:00
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.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $
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1999-08-28 00:22:10 +00:00
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.\" $FreeBSD$
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1997-05-12 12:13:10 +00:00
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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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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" notice, this list of conditions and the following disclaimer.
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.\" SUCH DAMAGE.
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.\"
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.Dd May 8, 1997
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.Dt CLOCK_GETTIME 2
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.Os BSD 4
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.Sh NAME
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.Nm clock_gettime ,
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.Nm clock_settime ,
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.Nm clock_getres
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.Nd get/set/calibrate date and time
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2000-04-21 09:42:15 +00:00
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.Sh LIBRARY
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.Lb libc
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1997-05-12 12:13:10 +00:00
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.Sh SYNOPSIS
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.Fd #include <sys/time.h>
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.Ft int
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.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp"
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.Ft int
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.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp"
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.Ft int
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1998-01-16 13:39:49 +00:00
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.Fn clock_getres "clockid_t clock_id" "struct timespec *tp"
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1997-05-12 12:13:10 +00:00
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.Sh DESCRIPTION
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The
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.Fn clock_gettime
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and
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.Fn clock_settime
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allow the calling process to retrieve or set the value used by a clock
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which is specifed by
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.Fa clock_id .
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.Pp
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.Fa clock_id
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can be one of three values: CLOCK_REALTIME for time that increments as
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a wall clock should, CLOCK_VIRTUAL for time that increments only when
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the CPU is running in user mode on behalf of the calling process, or
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CLOCK_PROF for time that increments when the CPU is running in user or
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kernel mode.
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.Pp
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The structure pointed to by
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.Fa tp
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is defined in
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.Ao Pa sys/time.h Ac
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as:
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.Pp
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.Bd -literal
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struct timespec {
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time_t tv_sec; /* seconds */
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long tv_nsec; /* and nanoseconds */
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};
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.Ed
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.Pp
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Only the super-user may set the time of day.
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If the system securelevel is greater than 1 (see
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.Xr init 8 ),
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the time may only be advanced.
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This limitation is imposed to prevent a malicious super-user
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from setting arbitrary time stamps on files.
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The system time can still be adjusted backwards using the
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.Xr adjtime 2
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system call even when the system is secure.
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.Pp
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The resolution (granularity) of a clock is returned by the
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.Fn clock_getres
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call. This value is placed in a (non-NULL)
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.Fa *tp .
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.Sh RETURN
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A 0 return value indicates that the call succeeded.
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A -1 return value indicates an error occurred, and in this
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case an error code is stored into the global variable
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.Va errno .
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.Sh ERRORS
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The following error codes may be set in
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.Va errno :
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.Bl -tag -width [EFAULT]
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.It Bq Er EINVAL
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The
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.Fa clock_id
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was not a valid value.
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.It Bq Er EFAULT
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The
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.Fa *tp
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argument address referenced invalid memory.
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.It Bq Er EPERM
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A user other than the super-user attempted to set the time.
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.El
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.Sh SEE ALSO
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.Xr date 1 ,
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.Xr adjtime 2 ,
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.Xr ctime 3 ,
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.Xr timed 8
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.Sh STANDARDS
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The
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.Fn clock_gettime ,
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etc.
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functions conform to
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.St -p1003.1b-93 .
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