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GETTIMEOFDAY(2) FreeBSD 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 *tp, struct timezone *tzp);
int
settimeofday(const struct timeval *tp, const struct timezone *tzp);
DESCRIPTION
The system's notion of the current Greenwich time and the current time
zone is obtained with the gettimeofday() system call, and set with the
settimeofday() system 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 {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* and microseconds */
};
struct timezone {
int tz_minuteswest; /* minutes west of Greenwich */
int tz_dsttime; /* type of dst correction */
};
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. The kernel generally does not track these values and they are
usually returned as zero. Use localtime(3) to find the offset for the
currently active timezone.
Only the super-user may set the time of day or time zone. If the system
is running at securelevel >= 2 (see init(8)), the time may only be
advanced or retarded by a maximum of one second. This limitation is
imposed to prevent a malicious super-user from setting arbitrary time
stamps on files. The system time can be adjusted backwards without
restriction using the adjtime(2) system call even when the system is
secure.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
SEE ALSO
date(1), adjtime(2), clock_gettime(2), ctime(3), timeradd(3), clocks(7)
HISTORY
The gettimeofday() system call appeared in 4.2BSD.
FreeBSD 14.0-RELEASE-p6 May 13, 2021 FreeBSD 14.0-RELEASE-p6