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GETTIMEOFDAY(2) System Calls Manual GETTIMEOFDAY(2)

gettimeofday, settimeofday
get/set date and time

library “libc”

#include <sys/time.h>

int
gettimeofday(struct timeval * restrict tp, void * restrict tzp);

int
settimeofday(const struct timeval * restrict tp, const void * restrict tzp);

Note: time zone information is no longer provided by this interface. See localtime(3) for information on how to retrieve it.

The system's notion of the current UTC time is obtained with the gettimeofday() call, and set with the settimeofday() call. The time is expressed in seconds and microseconds since midnight (0 hour), January 1, 1970. The resolution of the system clock is hardware dependent, and the time may be updated continuously or in “ticks”.

If tp is NULL, the time will not be returned or set. Despite being declared void *, the objects pointed to by tzp shall be of type struct timezone.

The structures pointed to by tp and tzp are defined in <sys/time.h>. The first one is described in timeval(3) and the latter legacy structure is defined as:

struct timezone {
	int	tz_minuteswest; /* of Greenwich */
	int	tz_dsttime;	/* type of dst correction to apply */
};

The timezone structure is provided only for source compatibility. It is ignored by settimeofday(), and gettimeofday() will always return zeroes.

If the calling user is not the super-user, then the settimeofday() function in the standard C library will try to use the clockctl(4) device if present, thus making possible for non privileged users to set the system time. If clockctl(4) is not present or not accessible, then settimeofday() reverts to the settimeofday() system call, which is restricted to the super user.

A return value 0 indicates that the call succeeded. A return value -1 indicates an error occurred, and in this case an error code is stored into the global variable errno.

The following error codes may be set in errno:
[]
An argument address referenced invalid memory.
[]
A user other than the super user attempted to set the time, or the specified time was less than the current time, which was not permitted at the current security level.

date(1), adjtime(2), ctime(3), localtime(3), clockctl(4), timed(8)

The gettimeofday() function call appeared in 4.2BSD. The tzp argument was deprecated in 4.4BSD (and many other systems).
May 18, 2010 NetBSD-7.0.1