1.\" $OpenBSD: clock_gettime.2,v 1.18 2007/12/09 10:30:14 brad 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. 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.Dd $Mdocdate: December 9 2007 $ 31.Dt CLOCK_GETTIME 2 32.Os 33.Sh NAME 34.Nm clock_gettime , 35.Nm clock_settime , 36.Nm clock_getres 37.Nd get/set/calibrate date and time 38.Sh SYNOPSIS 39.Fd #include <sys/time.h> 40.Ft int 41.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp" 42.Ft int 43.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp" 44.Ft int 45.Fn clock_getres "clockid_t clock_id" "struct timespec *tp" 46.Sh DESCRIPTION 47The 48.Fn clock_gettime 49and 50.Fn clock_settime 51allow the calling process to retrieve or set the value used by a clock 52which is specified by 53.Fa clock_id . 54.Pp 55.Fa clock_id 56can be one of four values: 57.Dv CLOCK_REALTIME 58for time that increments as 59a wall clock should, 60.Dv CLOCK_VIRTUAL 61for time that increments only when 62the CPU is running in user mode on behalf of the calling process, 63.Dv CLOCK_PROF 64for time that increments when the CPU is running in user or kernel mode, or 65.Dv CLOCK_MONOTONIC 66for time that increments at a steady rate (monotonically). 67.Pp 68The structure pointed to by 69.Fa tp 70is defined in 71.Aq Pa sys/time.h 72as: 73.Bd -literal -offset indent 74struct timespec { 75 time_t tv_sec; /* seconds */ 76 long tv_nsec; /* and nanoseconds */ 77}; 78.Ed 79.Pp 80Only the superuser may set the time of day. 81If the system securelevel is greater than 1 (see 82.Xr init 8 ) , 83the time may only be advanced. 84This limitation is imposed to prevent a malicious superuser 85from setting arbitrary time stamps on files. 86The system time can still be adjusted backwards using the 87.Xr adjtime 2 88system call even when the system is secure. 89.Pp 90The resolution (granularity) of a clock is returned by the 91.Fn clock_getres 92call. 93This value is placed in a (non-null) 94.Fa *tp . 95.Sh RETURN VALUES 96A 0 return value indicates that the call succeeded. 97A \-1 return value indicates an error occurred, and in this 98case an error code is stored into the global variable 99.Va errno . 100.Sh ERRORS 101The following error codes may be set in 102.Va errno : 103.Bl -tag -width Er 104.It Bq Er EINVAL 105The 106.Fa clock_id 107was not a valid value. 108.It Bq Er EFAULT 109The 110.Fa tp 111argument address referenced invalid memory. 112.It Bq Er EPERM 113A user other than the superuser attempted to set the time. 114.El 115.Sh SEE ALSO 116.Xr date 1 , 117.Xr adjtime 2 , 118.Xr ctime 3 , 119.Xr timed 8 120.Sh STANDARDS 121The 122.Fn clock_gettime , 123.Fn clock_settime , 124and 125.Fn clock_getres 126functions conform to 127.St -p1003.1b-93 . 128