Chrony is a pair of programs for maintaining the accuracy of computer
clocks.

The reference time can be derived from either Network Time Protocol
(NTP) servers (preferred), or wristwatch-and-keyboard (via chronyc).
The main source of information about the Network Time Protocol is
http://www.eecis.udel.edu/~ntp.

It is designed so that it can work on computers which only have
intermittent access to reference sources, for example computers which
use a dial-up account to access the Internet.  Of course, it will work
on computers with permanent connections too.

Chronyd can also operate as an RFC1305-compatible NTP server and peer.