Android Set System Time.

/framework/base/libs/utils/SystemClock.cpp:
#if HAVE_ANDROID_OS fd = open("/dev/alarm", O_RDWR); if(fd < 0) { LOGW("Unable to open alarm driver: %s\n", strerror(errno)); return -1; } ts.tv_sec = tv.tv_sec; ts.tv_nsec = tv.tv_usec * 1000; res = ioctl(fd, ANDROID_ALARM_SET_RTC, &ts); if(res < 0) { LOGW("Unable to set rtc to %ld: %s\n", tv.tv_sec, strerror(errno)); ret = -1; } close(fd); #else if (settimeofday(&tv, NULL) != 0) { LOGW("Unable to set clock to %d.%d: %s\n", (int) tv.tv_sec, (int) tv.tv_usec, strerror(errno)); ret = -1; } #endif 可以看到 Android 設定系統時間，用 ioctl，不能直接 call settimeofday.

settimeofday ，系統時間會改，但是 RTC 不會改， 所以 system reboot 後，時間還是沒變更。

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手動設會有 D/SystemClock( 2399): Setting time of day to sec=31622433 D/ ( 2269): enter Cmd: L D/dalvikvm( 2269): GC_CONCURRENT freed 1061K, 45% free 2224K/3971K, external 3688K/4325K, paused 3ms+3ms D/AlarmManagerService( 2269): Kernel timezone updated to -540 minutes west of GMT