NAME    [Toc]    [Back]

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

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <sys/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    [Toc]    [Back]

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

     The clock_id argument can be one of four values: CLOCK_REALTIME for time
     that increments as a wall clock should, CLOCK_MONOTONIC which increments
     in SI seconds, 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/time.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    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

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

STANDARDS    [Toc]    [Back]

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

BUGS    [Toc]    [Back]

     The CLOCK_VIRTUAL and CLOCK_PROF timers are not yet implemented.


FreeBSD 5.2.1		       February 5, 2003 		 FreeBSD 5.2.1