NTP client sync with its hardware clock

The example below shows how to make the sync more accurate. Edit the /etc/sysconfig/ntpd, which is the key configuration for ntpd. Add the line below

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# Set to 'yes' to sync hw clock after successful ntpdate.

SYNC_HWCLOCK=yes

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All servers have two kinds of clocks; the system clock and the hardware clock.The system clock is owned by the OS, and the hardware clock is owned by CMOS. When the Server is running, it usually provides it's system clock as the clock resource. However, when the server is shutdown, the system clock will sync to hardware and when rebooted the hardware clock will sync to system.The problem occurs because there may be some offset between the two clocks, if the server has been shutdown for a longtime and reboot again, the hardware clock may sync to system that may not be accurate.f SYNC_HWCLOCK=yes is used in /etc/sysconfig/ntpd, it means when the ntpd is started, it will first sync with hardware clock, that will reduce the offset and skew between the two clocks.