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.
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).