To configure the system clock to update the hardware clock, also known as the real-time clock (RTC), once after executing ntpdate, add the following line to /etc/sysconfig/ntpdate:

SYNC_HWCLOCK=yes

To update the hardware clock from the system clock, issue the following command as root:

~]# hwclock --systohc

When the system clock is being synchronized by ntpd, the kernel will in turn update the RTC every 11 minutes automatically.