date -s “2018-04-08 12:00:00” hwclock -r 修改完时间后，记得使用hwclock –w将系统时间同步到硬件时间。 hwclock -w 将系统时钟写入硬件时钟（hwclock -r 可以用来查看硬件时钟） at91_rtc f80480b0.rtc: setting system clock to 2012-01-01 00:04:47 UTC (1325376287) date -s “2017-04-08 12:00:00” hwclock –r 显示硬件时钟与日期
hwclock –s 将系统时钟调整为与目前的硬件时钟一致。
hwclock –w 将硬件时钟调整为与目前的系统时钟一致。 RTC - real time clock维护着系统的hardware时间，当linux启动时需要用RTC hardware时钟设置system 时间。 这个过程是在drivers/rtc/hctosys.c驱动中实现的，这个驱动实际只有一个init函数，并且把自己的init 函数声明为 late_initcall，这样可以保证RTC驱动已经正常运转。 init函数从RTC设备读取当前硬件时钟，然后调用do_settimeofday改写系统时钟。 static int __init rtc_hctosys(void) /home/xxx/ArmProject/multi-serial/kernel/SAMA_XIN2/drivers/rtc/hctosys.c * published by the Free Software Foundation. */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include /* IMPORTANT: the RTC only stores whole seconds. It is arbitrary * whether it stores the most close value or the value with partial * seconds truncated. However, it is important that we use it to store * the truncated value. This is because otherwise it is necessary, * in an rtc sync function, to read both xtime.tv_sec and * xtime.tv_nsec. On some processors (i.e. ARM), an atomic read * of >32bits is not possible. So storing the most close value would * slow down the sync API. So here we have the truncated value and * the best guess is to add 0.5s. */ static int __init rtc_hctosys(void) { int err = -ENODEV; struct rtc_time tm; struct timespec64 tv64 = { .tv_nsec = NSEC_PER_SEC >> 1, }; struct rtc_device *rtc = rtc_class_open(CONFIG_RTC_HCTOSYS_DEVICE); if (rtc == NULL) { pr_info("unable to open rtc device (%s) ", CONFIG_RTC_HCTOSYS_DEVICE); goto err_open; } err = rtc_read_time(rtc, &tm); if (err) { dev_err(rtc->dev.parent, "hctosys: unable to read the hardware clock "); goto err_read; } tv64.tv_sec = rtc_tm_to_time64(&tm); err = do_settimeofday64(&tv64); dev_info(rtc->dev.parent, "setting system clock to " "%d-%02d-%02d %02d:%02d:%02d UTC (%lld) ", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec, (long long) tv64.tv_sec); err_read: rtc_class_close(rtc); err_open: rtc_hctosys_ret = err; return err; } late_initcall(rtc_hctosys);