GETTIMEOFDAY(2) BSD Programmer's Manual GETTIMEOFDAY(2)NAME
gettimeofday, settimeofday - get/set date and time
SYNOPSIS
#include <time.h>
int
gettimeofday(struct timeval *tp, struct timezone *tzp);
int
settimeofday(const struct timeval *tp, const struct timezone *tzp);
DESCRIPTION
The timezone field is no longer used; timezone information is stored out-
side the kernel. See ctime(3) for more information.
The system's notion of the current Greenwich time and the current time
zone 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 or tzp is NULL, the associated time information will
not be returned or set.
The structures pointed to by tp and tzp are defined in <time.h> as:
struct timeval {
long tv_sec; /* seconds since Jan. 1, 1970 */
long tv_usec; /* and microseconds */
};
struct timezone {
int tz_minuteswest; /* of Greenwich */
int tz_dsttime; /* type of dst correction to apply */
};
The timezone structure indicates the local time zone (measured in minutes
of time westward from Greenwich), and a flag that, if nonzero, indicates
that Daylight Saving time applies locally during the appropriate part of
the year.
Only the super-user may set the time of day or time zone. If the system
is running in secure mode (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 se-
cure.
RETURN
A 0 return value indicates that the call succeeded. A -1 return value
indicates an error occurred, and in this case an error code is stored in-
to 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.
SEE ALSOdate(1), adjtime(2), ctime(3), timed(8)HISTORY
The gettimeofday function call appeared in 4.2BSD.
4th Berkeley Distribution May 26, 1995 2
