Description:

Hwclock is a program that runs under Linux and sets and queries the
Hardware Clock, which is often called the Real Time Clock, RTC, or
CMOS clock.

You can set the Hardware Clock to a particular time or from the Linux
System Time. You can set the Linux System Time from the Hardware
Clock, and a typical usage is to invoke Hwclock from a system startup
script to initialize the System Time.

Hwclock's --adjust function corrects systematic drift in the Hardware
Clock. You just invoke it regularly and it corrects for a fast or
slow Hardware Clock. Hwclock automatically computes how fast or slow
the Hardware Clock is every time you set it.

Hwclock uses /dev/rtc if it is available. Otherwise, it uses its own
direct I/O to do what the rtc device driver would normally do.