169 lines
4.9 KiB
Groff
169 lines
4.9 KiB
Groff
.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $
|
|
.\"
|
|
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 4. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd December 29, 2009
|
|
.Dt CLOCK_GETTIME 2
|
|
.Os
|
|
.Sh NAME
|
|
.Nm clock_gettime ,
|
|
.Nm clock_settime ,
|
|
.Nm clock_getres
|
|
.Nd get/set/calibrate date and time
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In time.h
|
|
.Ft int
|
|
.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp"
|
|
.Ft int
|
|
.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp"
|
|
.Ft int
|
|
.Fn clock_getres "clockid_t clock_id" "struct timespec *tp"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn clock_gettime
|
|
and
|
|
.Fn clock_settime
|
|
system calls allow the calling process to retrieve or set the value
|
|
used by a clock which is specified by
|
|
.Fa clock_id .
|
|
.Pp
|
|
The
|
|
.Fa clock_id
|
|
argument
|
|
can be one of the following values:
|
|
.Dv CLOCK_REALTIME ,
|
|
.Dv CLOCK_REALTIME_PRECISE ,
|
|
.Dv CLOCK_REALTIME_FAST
|
|
for time that increments as
|
|
a wall clock should;
|
|
.Dv CLOCK_MONOTONIC ,
|
|
.Dv CLOCK_MONOTONIC_PRECISE ,
|
|
.Dv CLOCK_MONOTONIC_FAST
|
|
which increments in SI seconds;
|
|
.Dv CLOCK_UPTIME ,
|
|
.Dv CLOCK_UPTIME_PRECISE ,
|
|
.Dv CLOCK_UPTIME_FAST
|
|
which starts at zero when the kernel boots and increments
|
|
monotonically in SI seconds while the machine is running;
|
|
.Dv CLOCK_VIRTUAL
|
|
for time that increments only when
|
|
the CPU is running in user mode on behalf of the calling process;
|
|
.Dv CLOCK_PROF
|
|
for time that increments when the CPU is running in user or
|
|
kernel mode; or
|
|
.Dv CLOCK_SECOND
|
|
which returns the current second without performing a full time counter
|
|
query, using in-kernel cached value of current second.
|
|
.Pp
|
|
The clock IDs
|
|
.Fa CLOCK_REALTIME_FAST ,
|
|
.Fa CLOCK_MONOTONIC_FAST ,
|
|
.Fa CLOCK_UPTIME_FAST
|
|
are analogs of corresponding IDs without _FAST suffix but do not perform
|
|
a full time counter query, so their accuracy is one timer tick.
|
|
Similarly,
|
|
.Fa CLOCK_REALTIME_PRECISE ,
|
|
.Fa CLOCK_MONOTONIC_PRECISE ,
|
|
.Fa CLOCK_UPTIME_PRECISE
|
|
are used to get the most exact value as possible, at the expense of
|
|
execution time.
|
|
.Pp
|
|
The structure pointed to by
|
|
.Fa tp
|
|
is defined in
|
|
.In sys/timespec.h
|
|
as:
|
|
.Bd -literal
|
|
struct timespec {
|
|
time_t tv_sec; /* seconds */
|
|
long tv_nsec; /* and nanoseconds */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
Only the super-user may set the time of day, using only
|
|
.Fa CLOCK_REALTIME .
|
|
If the system securelevel is greater than 1 (see
|
|
.Xr init 8 ) ,
|
|
the time may only be advanced.
|
|
This limitation is imposed to prevent a malicious super-user
|
|
from setting arbitrary time stamps on files.
|
|
The system time can still be adjusted backwards using the
|
|
.Xr adjtime 2
|
|
system call even when the system is secure.
|
|
.Pp
|
|
The resolution (granularity) of a clock is returned by the
|
|
.Fn clock_getres
|
|
system call.
|
|
This value is placed in a (non-NULL)
|
|
.Fa *tp .
|
|
.Sh RETURN VALUES
|
|
.Rv -std
|
|
.Sh ERRORS
|
|
The following error codes may be set in
|
|
.Va errno :
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
The
|
|
.Fa clock_id
|
|
argument
|
|
was not a valid value.
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa *tp
|
|
argument address referenced invalid memory.
|
|
.It Bq Er EPERM
|
|
A user other than the super-user attempted to set the time.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr date 1 ,
|
|
.Xr adjtime 2 ,
|
|
.Xr ctime 3 ,
|
|
.Xr timed 8
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn clock_gettime ,
|
|
.Fn clock_settime ,
|
|
and
|
|
.Fn clock_getres
|
|
system calls conform to
|
|
.St -p1003.1b-93 .
|
|
The clock IDs
|
|
.Fa CLOCK_REALTIME_FAST ,
|
|
.Fa CLOCK_REALTIME_PRECISE ,
|
|
.Fa CLOCK_MONOTONIC_FAST ,
|
|
.Fa CLOCK_MONOTONIC_PRECISE ,
|
|
.Fa CLOCK_UPTIME ,
|
|
.Fa CLOCK_UPTIME_FAST ,
|
|
.Fa CLOCK_UPTIME_PRECISE ,
|
|
.Fa CLOCK_SECOND
|
|
are FreeBSD extensions to the POSIX interface.
|