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Diffstat (limited to 'lib/libsys/clock_gettime.2')
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diff --git a/lib/libsys/clock_gettime.2 b/lib/libsys/clock_gettime.2 new file mode 100644 index 000000000000..89551d0f720b --- /dev/null +++ b/lib/libsys/clock_gettime.2 @@ -0,0 +1,241 @@ +.\" $OpenBSD: clock_gettime.2,v 1.4 1997/05/08 20:21:16 kstailey Exp $ +.\" +.\" Copyright (c) 1980, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.Dd August 10, 2024 +.Dt CLOCK_GETTIME 2 +.Os +.Sh NAME +.Nm clock_gettime , +.Nm clock_settime , +.Nm clock_getres +.Nd get/set/calibrate date and time +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In time.h +.Ft int +.Fn clock_gettime "clockid_t clock_id" "struct timespec *tp" +.Ft int +.Fn clock_settime "clockid_t clock_id" "const struct timespec *tp" +.Ft int +.Fn clock_getres "clockid_t clock_id" "struct timespec *tp" +.Sh DESCRIPTION +The +.Fn clock_gettime +and +.Fn clock_settime +system calls allow the calling process to retrieve or set the value +used by a clock which is specified by +.Fa clock_id . +.Pp +The +.Fa clock_id +argument can be a value obtained from +.Xr clock_getcpuclockid 3 +or +.Xr pthread_getcpuclockid 3 +as well as the following values: +.Pp +.Bl -tag -width indent -compact +.It Dv CLOCK_REALTIME +.It Dv CLOCK_REALTIME_PRECISE +.It Dv CLOCK_REALTIME_FAST +.It Dv CLOCK_REALTIME_COARSE +Increments in SI seconds like a wall clock. +It uses a 1970 epoch and implements the UTC timescale. +The count of physical SI seconds since 1970, adjusted by subtracting the number +of positive leap seconds and adding the number of negative leap seconds. +Behavior during a leap second is not defined by and POSIX standard. +.It Dv CLOCK_MONOTONIC +.It Dv CLOCK_MONOTONIC_PRECISE +.It Dv CLOCK_MONOTONIC_FAST +.It Dv CLOCK_MONOTONIC_COARSE +.It Dv CLOCK_BOOTTIME +Increments in SI seconds, even while the system is suspended. +Its epoch is unspecified. +The count is not adjusted by leap seconds. +.Fx implements +.It Dv CLOCK_UPTIME +.It Dv CLOCK_UPTIME_PRECISE +.It Dv CLOCK_UPTIME_FAST +Increments monotonically in SI seconds while the machine is running. +The count is not adjusted by leap seconds. +The epoch is unspecified. +.It Dv CLOCK_VIRTUAL +Increments only when +the CPU is running in user mode on behalf of the calling process. +.It Dv CLOCK_PROF +Increments when the CPU is running in user or kernel mode. +.It Dv CLOCK_SECOND +Returns the current second without performing a full time counter +query, using an in-kernel cached value of the current second. +.It Dv CLOCK_PROCESS_CPUTIME_ID +Returns the execution time of the calling process. +.It Dv CLOCK_THREAD_CPUTIME_ID +Returns the execution time of the calling thread. +.It Dv CLOCK_TAI +Increments in SI seconds like a wall clock. +It uses a 1970 epoch and implements the TAI timescale. +Similar to +.Dv CLOCK_REALTIME , +but without leap seconds. +It will increase monotonically during a leap second. +Will return +.Er EINVAL +if the current offset between TAI and UTC is not known, +which may be the case early in boot before NTP or other time daemon has +synchronized. +.El +.Pp +The clock IDs +.Dv CLOCK_BOOTTIME , +.Dv CLOCK_REALTIME , +.Dv CLOCK_TAI , +.Dv CLOCK_MONOTONIC , +and +.Dv CLOCK_UPTIME +perform a full time counter query. +The clock IDs with the _FAST suffix, i.e., +.Dv CLOCK_REALTIME_FAST , +.Dv CLOCK_MONOTONIC_FAST , +and +.Dv CLOCK_UPTIME_FAST , +do not perform +a full time counter query, so their accuracy is one timer tick. +Similarly, +.Dv CLOCK_REALTIME_PRECISE , +.Dv CLOCK_MONOTONIC_PRECISE , +and +.Dv CLOCK_UPTIME_PRECISE +are used to get the most exact value as possible, at the expense of +execution time. +The clock IDs +.Dv CLOCK_REALTIME_COARSE +and +.Dv CLOCK_MONOTONIC_COARSE +are aliases of corresponding IDs with _FAST suffix for compatibility with other +systems. +Finally, +.Dv CLOCK_BOOTTIME +is an alias for +.Dv CLOCK_MONOTONIC +for compatibility with other systems and is unrelated to the +.Fa kern.boottime +.Xr sysctl 8 . +.Pp +The structure pointed to by +.Fa tp +is defined in +.In sys/timespec.h +as: +.Bd -literal +struct timespec { + time_t tv_sec; /* seconds */ + long tv_nsec; /* and nanoseconds */ +}; +.Ed +.Pp +Only the super-user may set the time of day, using only +.Dv CLOCK_REALTIME . +If the system +.Xr securelevel 7 +is greater than 1 (see +.Xr init 8 ) , +the time may only be advanced. +This limitation is imposed to prevent a malicious super-user +from setting arbitrary time stamps on files. +The system time can still be adjusted backwards using the +.Xr adjtime 2 +system call even when the system is secure. +.Pp +The resolution (granularity) of a clock is returned by the +.Fn clock_getres +system call. +This value is placed in a (non-NULL) +.Fa *tp . +.Sh RETURN VALUES +.Rv -std +.Sh ERRORS +The following error codes may be set in +.Va errno : +.Bl -tag -width Er +.It Bq Er EINVAL +The +.Fa clock_id +or +.Fa timespec +argument +was not a valid value. +.It Bq Er EPERM +A user other than the super-user attempted to set the time. +.El +.Sh SEE ALSO +.Xr date 1 , +.Xr adjtime 2 , +.Xr clock_getcpuclockid 3 , +.Xr ctime 3 , +.Xr pthread_getcpuclockid 3 +.Sh STANDARDS +The +.Fn clock_gettime , +.Fn clock_settime , +and +.Fn clock_getres +system calls conform to +.St -p1003.1-2008 . +The clock IDs +.Dv CLOCK_BOOTTIME , +.Dv CLOCK_MONOTONIC_FAST , +.Dv CLOCK_MONOTONIC_PRECISE , +.Dv CLOCK_REALTIME_FAST , +.Dv CLOCK_REALTIME_PRECISE , +.Dv CLOCK_SECOND , +.Dv CLOCK_TAI , +.Dv CLOCK_UPTIME , +.Dv CLOCK_UPTIME_FAST , +and +.Dv CLOCK_UPTIME_PRECISE +are +.Fx +extensions to the POSIX interface. +.Pp +UTC is defined by ITU-R TF.460-6, Standard-frequency and time-signal emissions. +However, the +.Vt time_t +type is a simple count that does not provide a unique encoding for leap seconds, +nor a specification for what values should be used to encode a leap second. +.Pp +.Sh HISTORY +The +.Fn clock_gettime , +.Fn clock_settime , +and +.Fn clock_getres +system calls first appeared in +.Fx 3.0 . |