GETTIMEOFDAY(2) BSD System Calls Manual GETTIMEOFDAY(2)NAME
gettimeofday, settimeofday — get/set date and time
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/time.h>
int
gettimeofday(struct timeval * restrict tp, void * restrict tzp);
int
settimeofday(const struct timeval * restrict tp,
const void * restrict tzp);
DESCRIPTION
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() func‐
tion 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.
RETURN VALUES
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.
ERRORS
The following error codes may be set in errno:
[EFAULT] An argument address referenced invalid memory.
[EPERM] 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.
SEE ALSOdate(1), adjtime(2), ctime(3), localtime(3), clockctl(4), timed(8)HISTORY
The gettimeofday() function call appeared in 4.2BSD. The tzp argument
was deprecated in 4.4BSD (and many other systems).
BSD May 18, 2010 BSD
