1.\" $OpenBSD: clock_gettime.2,v 1.12 2000/10/18 05:12:08 aaron 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.Dd May 8, 1997 35.Dt CLOCK_GETTIME 2 36.Os 37.Sh NAME 38.Nm clock_gettime , 39.Nm clock_settime , 40.Nm clock_getres 41.Nd get/set/calibrate date and time 42.Sh SYNOPSIS 43.Fd #include <sys/time.h> 44.Ft int 45.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp" 46.Ft int 47.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp" 48.Ft int 49.Fn clock_getres "clockid_t clock_id" "struct timespec *tp" 50.Sh DESCRIPTION 51The 52.Fn clock_gettime 53and 54.Fn clock_settime 55allow the calling process to retrieve or set the value used by a clock 56which is specified by 57.Fa clock_id . 58.Pp 59.Fa clock_id 60can be one of three values: 61.Dv CLOCK_REALTIME 62for time that increments as 63a wall clock should, 64.Dv CLOCK_VIRTUAL 65for time that increments only when 66the CPU is running in user mode on behalf of the calling process, or 67.Dv CLOCK_PROF 68for time that increments when the CPU is running in user or kernel mode. 69.Pp 70The structure pointed to by 71.Fa tp 72is defined in 73.Ao Pa sys/time.h Ac 74as: 75.Pp 76.Bd -literal 77struct timespec { 78 time_t tv_sec; /* seconds */ 79 long tv_nsec; /* and nanoseconds */ 80}; 81.Ed 82.Pp 83Only the superuser may set the time of day. 84If the system securelevel is greater than 1 (see 85.Xr init 8 ) , 86the time may only be advanced. 87This limitation is imposed to prevent a malicious superuser 88from setting arbitrary time stamps on files. 89The system time can still be adjusted backwards using the 90.Xr adjtime 2 91system call even when the system is secure. 92.Pp 93The resolution (granularity) of a clock is returned by the 94.Fn clock_getres 95call. 96This value is placed in a (non-null) 97.Fa *tp . 98.Sh RETURN VALUES 99A 0 return value indicates that the call succeeded. 100A \-1 return value indicates an error occurred, and in this 101case an error code is stored into the global variable 102.Va errno . 103.Sh ERRORS 104The following error codes may be set in 105.Va errno : 106.Bl -tag -width [EFAULT] 107.It Bq Er EINVAL 108The 109.Fa clock_id 110was not a valid value. 111.It Bq Er EFAULT 112The 113.Fa *tp 114argument address referenced invalid memory. 115.It Bq Er EPERM 116A user other than the superuser attempted to set the time. 117.El 118.Sh SEE ALSO 119.Xr date 1 , 120.Xr adjtime 2 , 121.Xr ctime 3 , 122.Xr timed 8 123.Sh STANDARDS 124The 125.Fn clock_gettime , 126.Fn clock_settime , 127and 128.Fn clock_setres 129functions conform to 130.St -p1003.1b-93 . 131