1.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $ 2.\" $FreeBSD: src/lib/libc/sys/clock_gettime.2,v 1.3.2.8 2001/12/14 18:34:00 ru Exp $ 3.\" $DragonFly: src/lib/libc/sys/clock_gettime.2,v 1.6 2008/05/02 02:05:04 swildner Exp $ 4.\" 5.\" Copyright (c) 1980, 1991, 1993 6.\" The Regents of the University of California. All rights reserved. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.Dd May 8, 1997 33.Dt CLOCK_GETTIME 2 34.Os 35.Sh NAME 36.Nm clock_gettime , 37.Nm clock_settime , 38.Nm clock_getres 39.Nd get/set/calibrate date and time 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In 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 two values: 61.Dv CLOCK_REALTIME 62for time that increments as a wall clock should and 63.Dv CLOCK_MONOTONIC 64for time that increments at a static rate in SI seconds. 65.Pp 66The structure pointed to by 67.Fa tp 68is defined in 69.In sys/time.h 70as: 71.Bd -literal 72struct timespec { 73 time_t tv_sec; /* seconds */ 74 long tv_nsec; /* and nanoseconds */ 75}; 76.Ed 77.Pp 78Only the super-user may set the time of day. 79If the system securelevel is greater than 1 (see 80.Xr init 8 ) , 81the time may only be advanced. 82This limitation is imposed to prevent a malicious super-user 83from setting arbitrary time stamps on files. 84The system time can still be adjusted backwards using the 85.Xr adjtime 2 86system call even when the system is secure. 87.Pp 88The resolution (granularity) of a clock is returned by the 89.Fn clock_getres 90call. This value is placed in a (non-NULL) 91.Fa *tp . 92.Sh RETURN VALUES 93.Rv -std 94.Sh ERRORS 95The following error codes may be set in 96.Va errno : 97.Bl -tag -width Er 98.It Bq Er EINVAL 99The 100.Fa clock_id 101was not a valid value. 102.It Bq Er EFAULT 103The 104.Fa *tp 105argument address referenced invalid memory. 106.It Bq Er EPERM 107A user other than the super-user attempted to set the time. 108.El 109.Sh SEE ALSO 110.Xr date 1 , 111.Xr adjtime 2 , 112.Xr ctime 3 , 113.Xr timed 8 114.Sh STANDARDS 115The 116.Fn clock_gettime , 117etc.\& 118functions conform to 119.St -p1003.1b-93 . 120