settimeofday() - set date and time
#include <sys/time.h>
int settimeofday (struct timeval *tp, void *tzp)
Note
The system's notion of the current Greenwich time and the current time zone is obtained with the gettimeofday(2) 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 superuser may set the time of day or time zone. If the system is running in secure mode (see init), 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() system call even when the system is secure.
The function returns 0 on success. On failure, they return -1 and set the global variable errno to indicate the error.
The following error codes may be set in errno:
gettimeofday(2)
date(1)
ctime(3)