CLOCK_GETTIME(2) BSD 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 <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
The clock_gettime() and clock_settime() allow the calling process to
retrieve or set the value used by a clock which is specified by clock_id.
clock_id can be one of two values: CLOCK_REALTIME for time that incre‐
ments as a wall clock should and CLOCK_MONOTONIC for time that increments
at a static rate in SI seconds.
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()
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 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 ALSOdate(1), adjtime(2), ctime(3), timed(8)STANDARDS
The clock_gettime(), etc. functions conform to IEEE Std 1003.1b-1993
(“POSIX.1”).
BSD May 8, 1997 BSD
