rclockd is a unix daemon which will systematically update the system time with the time received from a radio clock attached to the serial port.
Depends only on pthreads and the date command. Manpages and usage instructions are included in the tarball.
Installation should just be a matter of:
./configure make make install
An example rc init script is built in the scripts/ folder. It is compatible with redhat based systems and supports chkconfig. Just copy to /etc/init.d and run chkconfig --add rclockd to set up the boot script on redhat based systems.