This is the README for chrony.

What is chrony?

chrony is a versatile implementation of the Network Time Protocol (NTP). It can synchronise the system clock with NTP servers, reference clocks (e.g. GPS receiver), and manual input using wristwatch and keyboard. It can also operate as an NTPv4 (RFC 5905) server and peer to provide a time service to other computers in the network.

It is designed to perform well in a wide range of conditions, including intermittent network connections, heavily congested networks, changing temperatures (ordinary computer clocks are sensitive to temperature), and systems that do not run continuosly, or run on a virtual machine.

Typical accuracy between two machines synchronised over the Internet is within a few milliseconds; on a LAN, accuracy is typically in tens of microseconds. With hardware timestamping, or a hardware reference clock, sub-microsecond accuracy may be possible.

Two programs are included in chrony, chronyd is a daemon that can be started at boot time and chronyc is a command-line interface program which can be used to monitor chronyd's performance and to change various operating parameters whilst it is running.

What will chrony run on?

The software is known to work on Linux, FreeBSD, NetBSD, macOS and illumos. Closely related systems may work too. Any other system will likely require a porting exercise.

How do I set it up?

The file INSTALL gives instructions. On supported systems the compilation process should be automatic. You will need a C compiler, e.g. gcc or clang.

What documentation is there?

The distribution includes manual pages and a document containing Frequently Asked Questions (FAQ).

The documentation is also available on the chrony web pages, accessible through the URL

https://chrony.tuxfamily.org/

Where are new versions announced?

There is a low volume mailing list where new versions and other important news relating to chrony are announced. You can join this list by sending mail with the subject "subscribe" to

[email protected]

How can I get support for chrony?

There are two other mailing lists relating to chrony. chrony-users is a discussion list for users, e.g. for questions about chrony configuration and bug reports. chrony-dev is a more technical list for developers, e.g. for submitting patches and discussing how new features should be implemented. To subscribe to either of these lists, send a message with the subject "subscribe" to

[email protected] or [email protected]

as applicable.

License

chrony is distributed under the GNU General Public License version 2.

Authors

Richard P. Curnow [email protected] Miroslav Lichvar [email protected]

Acknowledgements

In writing the chronyd program, extensive use has been made of the NTPv3 (RFC 1305) and NTPv4 (RFC 5905) specification. The source code of the xntpd/ntpd implementation written by Dennis Fergusson, Lars Mathiesen, David Mills, and others has been used to check the details of the protocol.

The following people have provided patches and other major contributions to chrony:

Lonnie Abelbeck [email protected] Benny Lyne Amorsen [email protected] Andrew Bishop [email protected] Vincent Blut [email protected] Stephan I. Boettcher [email protected] David Bohman [email protected] Goswin Brederlow [email protected] Leigh Brown [email protected] Erik Bryer [email protected] Jonathan Cameron [email protected] Bryan Christianson [email protected] Juliusz Chroboczek [email protected] Kamil Dudka [email protected] Christian Ehrhardt [email protected] Paul Elliott [email protected] Robert Fairley [email protected] Stefan R. Filipek [email protected] Mike Fleetwood [email protected] Alexander Gretencord [email protected] Andrew Griffiths [email protected] Walter Haidinger [email protected] Juergen Hannken-Illjes [email protected] John Hasler [email protected] Tjalling Hattink [email protected] Liam Hatton [email protected] Jachym Holecek [email protected] Håkan Johansson [email protected] Jim Knoble [email protected] Antti Jrvinen [email protected] Uwe Kleine-König [email protected] Eric Lammerts [email protected] Stefan Lucke [email protected] Victor Lum [email protected] Kevin Lyda [email protected] Paul Menzel [email protected] Vladimir Michl [email protected] Victor Moroz [email protected] Kalle Olavi Niemitalo [email protected] Frank Otto [email protected] Denny Page [email protected] Chris Perl [email protected] Gautier PHILIPPON [email protected] Andreas Piesk [email protected] Baruch Siach [email protected] Foster Snowhill [email protected] Andreas Steinmetz [email protected] NAKAMURA Takumi [email protected] Timo Teras [email protected] Bill Unruh [email protected] Stephen Wadeley [email protected] Bernhard Weiss [email protected] Wolfgang Weisselberg [email protected] Bernhard M. Wiedemann [email protected] Joachim Wiedorn [email protected] Ralf Wildenhues [email protected] Ulrich Windl [email protected] Michael Witten [email protected] Doug Woodward [email protected] Thomas Zajic [email protected]

Many other people have contributed bug reports and suggestions. We are sorry we cannot identify all of you individually.