clock_settime() sets the clock clock_id to the value specified by tp. clock_settime() truncates time values that are between resolution multiples to the smaller resolution multiple clock_settime() supports CLOCK_REALTIME If clock_settime() changes the time for CLOCK_REALTIME, then any absolute timers will use the new time for expiration. If at this point, the timer should have expired in the past, it will expire immediately (no error). clock_settime() does not affect _relative_ timers (either timers or nanosleep() calls). These expire when the relative time interval elapses, regardless of what the clock says. clock_settime() cannot set the monotonic clock CLOCK_MONOTONIC and will fail if invoked with clock_id CLOCK_MONOTONIC If clock_settime() changes the time for CLOCK_REALTIME, then any threads blocked on clock_nanosleep() for the CLOCK_REALTIME clock will use the new time for expiration. If at this point, the timer should have expired in the past, it will expire immediately (no error). clock_settime() does not affect clock_nanosleep() _relative_ timers. These expire when the relative time interval elapses, regardless of what the clock says. If _POSIX_CPUTIME is defined, clock_settime() supports clock_ids obtained via clock_getcpuclockid(). The value set is the amount of execution time of the process associated with the clock. If _POSIX_CPUTIME is defined, clock_settime() supports clock_id CLOCK_PROCESS_CPUTIME_ID (= the CPU clock of the calling process). The value set is the amount of execution time of the calling process. If clock_settime() is used to change the value of a CPU-time clock, sporadic server scheduling policy is unaffected. If _POSIX_THREAD_CPUTIME is defined, clock_settime() supports clock_ids obtained via pthread_getcpuclockid(). The value set is the amount of execution time of the thread associated with the clock. If _POSIX_THREAD_CPUTIME is defined, clock_settime() supports clock_id CLOCK_THREAD_CPUTIME_ID (= the CPU clock of the calling thread). The value set is the amount of execution time of the calling thread. If clock_settime() is used to change the value of a CPU-time clock, sporadic server scheduling policy is unaffected. clock_settime() returns 0 on success clock_settime() returns -1 on failure clock_settime() sets errno=EINVAL if clock_id does not specify a known clock clock_settime() sets errno=EINVAL if tp is outside the valid range for clock_id clock_settime() sets errno=EINVAL if tp has a nsec value below 0 or above (or equal to) 1000 million clock_settime() sets errno=EINVAL if clock_id is CLOCK_MONOTONIC clock_settime() sets errno=EPERM if the calling process does not have privileges to set clockid (MAY, not SHOULD).