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CLOCK_SETTIME(2)              System Calls Manual             CLOCK_SETTIME(2)

NAME
     clock_settime, clock_gettime, clock_getres - clock and timer functions

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <time.h>

     int
     clock_settime(clockid_t clock_id, const struct timespec *tp);

     int
     clock_gettime(clockid_t clock_id, struct timespec *tp);

     int
     clock_getres(clockid_t clock_id, struct timespec *res);

DESCRIPTION
     The clock_settime() function sets the clock identified by clock_id to the
     absolute time specified by tp.  If the time specified by tp is not a
     multiple of the resolution of the clock, tp is truncated to a multiple of
     the resolution.

     The clock_gettime() function stores the time of the clock identified by
     clock_id into the location specified by tp.

     The clock_getres() function stores the resolution of the clock identified
     by clock_id into the location specified by res, unless res is NULL.

     The following clock_id values are supported:

     CLOCK_REALTIME   identifies the realtime clock for the system.  For this
                      clock, the values specified by clock_settime() and
                      obtained by clock_gettime() represent the amount of time
                      (in seconds and nanoseconds) since 00:00 Universal
                      Coordinated Time, January 1, 1970.

     CLOCK_MONOTONIC  identifies a clock that increases at a steady rate
                      (monotonically).  This clock is not affected by calls to
                      adjtime(2) and settimeofday(2) and will fail with an
                      EINVAL error if it's the clock specified in a call to
                      clock_settime().  The origin of the clock is
                      unspecified.

     CLOCK_VIRTUAL    identifies a clock that increments only when the CPU is
                      running in user mode on behalf of the calling process.

     CLOCK_PROF       identifies a clock that increments when the CPU is
                      running in user or kernel mode on behalf of the calling
                      process.

     CLOCK_PROCESS_CPUTIME_ID
                      identifies a per process clock based on tick values.
                      This clock is not settable.

     CLOCK_THREAD_CPUTIME_ID
                      identifies a per thread clock based on tick values.
                      This clock is not settable.

     If the calling user is not the super-user, the clock_settime() system
     call will fail, and the clock_settime() function in the standard C
     library will try to use the clockctl(4) device if present, thus making it
     possible for non privileged users to set the system time.  If clockctl(4)
     is not present or not accessible, then clock_settime() returns EPERM.

RETURN VALUES
     A value of 0 is returned on success.  Otherwise, a value of -1 is
     returned and errno is set to indicate the error.

ERRORS
     The clock_settime(), clock_gettime() and clock_getres() functions will
     fail if:

     [EINVAL]           The clock_id argument does not specify a known clock.

     [ENOSYS]           The function is not supported by this implementation.

     The clock_settime() function will fail if:

     [EINVAL]           The tp argument is outside the range for the specified
                        clock, clock_id; or the tp argument specified a
                        nanosecond value less than zero of greater than or
                        equal 1000 million; or the clock_id argument is a
                        clock that can not be adjusted.

     [EPERM]            The calling process does not have the appropriate
                        privilege to set the specified clock, clock_id.

     The clock_gettime() function will fail if:

     [EFAULT]           The tp argument specifies an address that is not a
                        valid part of the process address space.

SEE ALSO
     ctime(3), time(3), clockctl(4)

STANDARDS
     The clock_settime(), clock_gettime() and clock_getres() functions conform
     to IEEE Std 1003.1b-1993 ("POSIX.1b").

NetBSD 10.99                  September 23, 2016                  NetBSD 10.99