Description

   The clock_settime function sets the specified clock, clock_id,
   to the value specified by tp. Time values that are between two
   consecutive non-negative integer multiples of the resolution of
   the specified clock are truncated down to the smaller multiple of
   the resolution.

   A clock can be systemwide (that is, visible to all processes)
   or per-process (measuring time that is meaningful only within a
   process).

   The CLOCK_REALTIME clock, defined in <time.h>, represents the
   realtime clock for the system. For this clock, the values
   specified by clock_settime and returned by clock_gettime
   represent the amount of time elapsed, in seconds and nanoseconds,
   since the Epoch. The Epoch is defined as 00:00:00:00 January 1,
   1970 Greenwich Mean Time (GMT).

   You must have OPER, LOG_IO, and SYSPRV privileges to use the
   clock_settime function.

   On success, the function returns 0.

   On failure, the function returns -1 and sets errno to indicate
   the error.

   See also clock_getres, clock_gettime, time, and ctime.