#include <unistd.h>int stime(const time_t *tp);
The stime() function sets the system's idea of the time and date. The tp argument points to the value of time as measured in seconds from 00:00:00 UTC January 1, 1970.
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The stime() function will fail if:
The tp argument points to an invalid (negative) time value.
The effective user of the calling process is not super-user.