1.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey 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.\" 4. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" $FreeBSD$ 31.\" 32.Dd November 4, 2006 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 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 55system calls allow the calling process to retrieve or set the value 56used by a clock which is specified by 57.Fa clock_id . 58.Pp 59The 60.Fa clock_id 61argument 62can be one of five values: 63.Dv CLOCK_REALTIME 64for time that increments as 65a wall clock should, 66.Dv CLOCK_MONOTONIC 67which increments in SI seconds, 68.Dv CLOCK_UPTIME 69which starts at zero when the kernel boots and increments 70monotonically in SI seconds while the machine is running, 71.Dv CLOCK_VIRTUAL 72for time that increments only when 73the CPU is running in user mode on behalf of the calling process, or 74.Dv CLOCK_PROF 75for time that increments when the CPU is running in user or 76kernel mode. 77.Pp 78The structure pointed to by 79.Fa tp 80is defined in 81.In sys/timespec.h 82as: 83.Pp 84.Bd -literal 85struct timespec { 86 time_t tv_sec; /* seconds */ 87 long tv_nsec; /* and nanoseconds */ 88}; 89.Ed 90.Pp 91Only the super-user may set the time of day. 92If the system securelevel is greater than 1 (see 93.Xr init 8 ) , 94the time may only be advanced. 95This limitation is imposed to prevent a malicious super-user 96from setting arbitrary time stamps on files. 97The system time can still be adjusted backwards using the 98.Xr adjtime 2 99system call even when the system is secure. 100.Pp 101The resolution (granularity) of a clock is returned by the 102.Fn clock_getres 103system call. 104This value is placed in a (non-NULL) 105.Fa *tp . 106.Sh RETURN VALUES 107.Rv -std 108.Sh ERRORS 109The following error codes may be set in 110.Va errno : 111.Bl -tag -width Er 112.It Bq Er EINVAL 113The 114.Fa clock_id 115argument 116was not a valid value. 117.It Bq Er EFAULT 118The 119.Fa *tp 120argument address referenced invalid memory. 121.It Bq Er EPERM 122A user other than the super-user attempted to set the time. 123.El 124.Sh SEE ALSO 125.Xr date 1 , 126.Xr adjtime 2 , 127.Xr ctime 3 , 128.Xr timed 8 129.Sh STANDARDS 130The 131.Fn clock_gettime , 132.Fn clock_settime , 133and 134.Fn clock_getres 135system calls conform to 136.St -p1003.1b-93 . 137