嵌入式Linux 设置时间和日期 API ，是busybox中提取的源码；

Linux设置时间和日期步骤是：

1. 设置系统时间和日期；

2. 将系统的时间和日期，同步到硬件中；

#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <time.h>
#include <linux/rtc.h>
#include <linux/capability.h> 



int  SetSysDateAndTime(const char *time_str);
void SetHWClockFromSysClock(int utc);

static int  rtc_xopen(const char **default_rtc, int flags);
static void write_rtc(time_t t, int utc);


static const char *rtcname;



int main(void)
{
	const char time_str[] = "1989-11-22 11:22:33";
	SetSysDateAndTime(time_str);
	SetHWClockFromSysClock(0);
	
	system("reboot");
	
	return 0;
}


int SetSysDateAndTime(const char *time_str)
{
    struct tm 			time_tm;
    struct timeval 	time_tv;
    time_t 					timep;
		int 						ret;
		
		if(time_str == NULL)
		{
				fprintf(stderr, "time string args invalid!\n");
				return -1;
		}
	
    sscanf(time_str, "%d-%d-%d %d:%d:%d", &time_tm.tm_year, &time_tm.tm_mon, &time_tm.tm_mday, &time_tm.tm_hour, &time_tm.tm_min, &time_tm.tm_sec);
    time_tm.tm_year 	-= 1900;
    time_tm.tm_mon 		-= 1;
    time_tm.tm_wday 	= 0;
    time_tm.tm_yday 	= 0;
    time_tm.tm_isdst	= 0;

    timep = mktime(&time_tm);
    time_tv.tv_sec  = timep;
    time_tv.tv_usec = 0;

    ret = settimeofday(&time_tv, NULL);
    if(ret != 0)
    {
        fprintf(stderr, "settimeofday failed\n");
        return -2;
    }
	
	return 0;
}


void SetHWClockFromSysClock(int utc)
{
	struct timeval tv;

	gettimeofday(&tv, NULL);
	//if (gettimeofday(&tv, NULL))
	//	bb_perror_msg_and_die("gettimeofday() failed");
	write_rtc(tv.tv_sec, utc);
}



static int  rtc_xopen(const char **default_rtc, int flags)
{
	int rtc;

	if (!*default_rtc) {
		*default_rtc = "/dev/rtc";
		rtc = open(*default_rtc, flags);
		if (rtc >= 0)
			return rtc;
		*default_rtc = "/dev/rtc0";
		rtc = open(*default_rtc, flags);
		if (rtc >= 0)
			return rtc;
		*default_rtc = "/dev/misc/rtc";
	}

	return open(*default_rtc, flags);
}

static void write_rtc(time_t t, int utc)
{
#define RTC_SET_TIME	_IOW('p', 0x0a, struct rtc_time) /* Set RTC time    */

	struct tm tm;
	int rtc = rtc_xopen(&rtcname, O_WRONLY);

	tm = *(utc ? gmtime(&t) : localtime(&t));
	tm.tm_isdst = 0;

	ioctl(rtc, RTC_SET_TIME, &tm);

	close(rtc);
}

Linux 设置系统时间和日期 API