NAME
gettimeofday,
settimeofday —
get/set date and time
LIBRARY
library “libc”
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
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.
The
settimeofday()
system call is available only for the super-user. If the calling user is not
the super-user, the system call will fail, and the
settimeofday() function in the standard C library
will try to use the
clockctl(4) device if present, thus making it possible for non
privileged users to set the system time. If
clockctl(4) is not present or not accessible, then
settimeofday() returns
EPERM.
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 ALSO
date(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).