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CLOCK_GETTIME(2)	  FreeBSD System Calls Manual	      CLOCK_GETTIME(2)

NAME
     clock_gettime, clock_settime, clock_getres	-- get/set/calibrate date and
     time

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <time.h>

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

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

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

DESCRIPTION
     The clock_gettime() and clock_settime() system calls allow	the calling
     process to	retrieve or set	the value used by a clock which	is specified
     by	clock_id.

     The clock_id argument can be one of five values: CLOCK_REALTIME for time
     that increments as	a wall clock should, CLOCK_MONOTONIC which increments
     in	SI seconds, CLOCK_UPTIME which starts at zero when the kernel boots
     and increments monotonically in SI	seconds	while the machine is running,
     CLOCK_VIRTUAL for time that increments only when the CPU is running in
     user mode on behalf of the	calling	process, or CLOCK_PROF for time	that
     increments	when the CPU is	running	in user	or kernel mode.

     The structure pointed to by tp is defined in <sys/timespec.h> as:

     struct timespec {
	     time_t  tv_sec;	     /*	seconds	*/
	     long    tv_nsec;	     /*	and nanoseconds	*/
     };

     Only the super-user may set the time of day.  If the system securelevel
     is	greater	than 1 (see 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 adjtime(2) system call	even when the system is
     secure.

     The resolution (granularity) of a clock is	returned by the	clock_getres()
     system call.  This	value is placed	in a (non-NULL)	*tp.

RETURN VALUES
     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

ERRORS
     The following error codes may be set in errno:

     [EINVAL]		The clock_id argument was not a	valid value.

     [EFAULT]		The *tp	argument address referenced invalid memory.

     [EPERM]		A user other than the super-user attempted to set the
			time.

SEE ALSO
     date(1), adjtime(2), ctime(3), timed(8)

STANDARDS
     The clock_gettime(), clock_settime(), and clock_getres() system calls
     conform to	IEEE Std 1003.1b-1993 (``POSIX.1'').

FreeBSD	11.1		       November	4, 2006			  FreeBSD 11.1
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS

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