GETTIMEOFDAY(2) OpenBSD Programmer's Manual GETTIMEOFDAY(2)NAME
gettimeofday, settimeofday - get/set date and time
SYNOPSIS
#include <sys/time.h>
int
gettimeofday(struct timeval *tp, struct timezone *tzp);
int
settimeofday(const struct timeval *tp, const struct timezone *tzp);
DESCRIPTION
Note: timezone is no longer used; this information is kept outside the
kernel.
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 <sys/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 superuser may set the time of day or time zone. If the system
securelevel is greater than 1 (see init(8)), the time may only be
advanced. This limitation is imposed to prevent a malicious superuser
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 secure.
RETURN VALUES
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
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 superuser attempted to set the time.
SEE ALSOdate(1), adjtime(2), getitimer(2), ctime(3), timed(8)HISTORY
The gettimeofday() function call appeared in 4.2BSD.
CAVEATS
Setting the time with settimeofday() is dangerous; if possible use
adjtime(2) instead. Many daemon programming techniques utilize time-
delta techniques using the results from gettimeofday() instead of from
clock_gettime(2) on the CLOCK_MONOTONIC clock. Time jumps can cause
these programs to malfunction in unexpected ways. If the time must be
set, consider rebooting the machine for safety.
OpenBSD 4.9 April 1, 2010 OpenBSD 4.9
