1 .\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $
3 .\" Copyright (c) 1980, 1991, 1993
4 .\" The Regents of the University of California. All rights reserved.
6 .\" Redistribution and use in source and binary forms, with or without
7 .\" modification, are permitted provided that the following conditions
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.
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
37 .Nd get/set/calibrate date and time
43 .Fn clock_gettime "clockid_t clock_id" "struct timespec *tp"
45 .Fn clock_settime "clockid_t clock_id" "const struct timespec *tp"
47 .Fn clock_getres "clockid_t clock_id" "struct timespec *tp"
53 system calls allow the calling process to retrieve or set the value
54 used by a clock which is specified by
59 argument can be a value obtained from
60 .Xr clock_getcpuclockid 3
62 .Xr pthread_getcpuclockid 3
63 as well as the following values:
65 .Bl -tag -width indent -compact
67 .It Dv CLOCK_REALTIME_PRECISE
68 .It Dv CLOCK_REALTIME_FAST
69 .It Dv CLOCK_REALTIME_COARSE
70 Increments as a wall clock should.
71 .It Dv CLOCK_MONOTONIC
72 .It Dv CLOCK_MONOTONIC_PRECISE
73 .It Dv CLOCK_MONOTONIC_FAST
74 .It Dv CLOCK_MONOTONIC_COARSE
75 Increments in SI seconds.
77 .It Dv CLOCK_UPTIME_PRECISE
78 .It Dv CLOCK_UPTIME_FAST
80 Starts at zero when the kernel boots and increments
81 monotonically in SI seconds while the machine is running.
84 the CPU is running in user mode on behalf of the calling process.
86 Increments when the CPU is running in user or kernel mode.
88 Returns the current second without performing a full time counter
89 query, using an in-kernel cached value of the current second.
90 .It Dv CLOCK_PROCESS_CPUTIME_ID
91 Returns the execution time of the calling process.
92 .It Dv CLOCK_THREAD_CPUTIME_ID
93 Returns the execution time of the calling thread.
101 perform a full time counter query.
102 The clock IDs with the _FAST suffix, i.e.,
103 .Fa CLOCK_REALTIME_FAST ,
104 .Fa CLOCK_MONOTONIC_FAST ,
106 .Fa CLOCK_UPTIME_FAST ,
108 a full time counter query, so their accuracy is one timer tick.
110 .Fa CLOCK_REALTIME_PRECISE ,
111 .Fa CLOCK_MONOTONIC_PRECISE ,
113 .Fa CLOCK_UPTIME_PRECISE
114 are used to get the most exact value as possible, at the expense of
117 .Fa CLOCK_REALTIME_COARSE
119 .Fa CLOCK_MONOTONIC_COARSE
120 are aliases of corresponding IDs with _FAST suffix for compatibility with other
126 for compatibility with other systems.
128 The structure pointed to by
135 time_t tv_sec; /* seconds */
136 long tv_nsec; /* and nanoseconds */
140 Only the super-user may set the time of day, using only
144 is greater than 1 (see
146 the time may only be advanced.
147 This limitation is imposed to prevent a malicious super-user
148 from setting arbitrary time stamps on files.
149 The system time can still be adjusted backwards using the
151 system call even when the system is secure.
153 The resolution (granularity) of a clock is returned by the
156 This value is placed in a (non-NULL)
161 The following error codes may be set in
170 was not a valid value.
172 A user other than the super-user attempted to set the time.
177 .Xr clock_getcpuclockid 3 ,
179 .Xr pthread_getcpuclockid 3
186 system calls conform to
189 .Fa CLOCK_REALTIME_FAST ,
190 .Fa CLOCK_REALTIME_PRECISE ,
191 .Fa CLOCK_MONOTONIC_FAST ,
192 .Fa CLOCK_MONOTONIC_PRECISE ,
194 .Fa CLOCK_UPTIME_FAST ,
195 .Fa CLOCK_UPTIME_PRECISE ,
199 extensions to the POSIX interface.
206 system calls first appeared in