Copyright (c) 1980 Regents of the University of California.
All rights reserved. The Berkeley software License Agreement
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@(#)gettimeofday.2 6.2 (Berkeley) 06/05/85

C 4 gettimeofday, settimeofday - get/set date and time

#include <sys/time.h>

gettimeofday(tp, tzp)
struct timeval *tp;
struct timezone *tzp;

settimeofday(tp, tzp)
struct timeval *tp;
struct timezone *tzp;

Gettimeofday returns the system's notion of the current Greenwich time, and if tzp is nonzero, the current time zone. Time returned is expressed relative in seconds and microseconds since midnight January 1, 1970.

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.

If tzp is zero settimeofday does not change the current time zone. Only the super-user may set the time of day.

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. The following error codes may be set in errno:

15 [EFAULT] An argument address referenced invalid memory.

15 [EPERM] A user other than the super-user attempted to set the time.

date(1), netdate(1), adjtime(2), ctime(3), timedaemon(8) Time is never correct enough to believe the microsecond values, although the timedaemon mechanism allows local clusters of systems to synchronize their clocks to within a few milliseconds.