Linux Time and Clocks...
There are two clocks in your computer. The hardware (CMOS) clock runs even when the computer is turned off, and is used when the system starts up and by DOS (if you use DOS). The ordinary system time, shown and set by date, is maintained by the kernel while Linux is running.
You can display the CMOS clock time, or set either clock from the other,
with /sbin/clock (or hwclock).
There are various other programs that can...
