GETTIMEOFDAY(2)

NAME
gettimeofday, settimeofday - get/set date and time

LIBRARY
libc

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; /* 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.

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 secure.

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 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.

SEE ALSO
date(1), adjtime(2), ctime(3), clocks(7), timed(8)

HISTORY
The gettimeofday() function call appeared in 4.2BSD.