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 continuously, 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, OpenBSD, 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-project.org/

License

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

Authors

Richard P. Curnow rc@rc0.org.uk Miroslav Lichvar mlichvar@redhat.com

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 lonnie@abelbeck.com Benny Lyne Amorsen benny@amorsen.dk Andrew Bishop amb@gedanken.demon.co.uk Vincent Blut vincent.debian@free.fr Luca Boccassi bluca@debian.org Stephan I. Boettcher stephan@nevis1.columbia.edu David Bohman debohman@gmail.com Anthony Brandon anthony@amarulasolutions.com Goswin Brederlow brederlo@informatik.uni-tuebingen.de Leigh Brown leigh@solinno.co.uk Erik Bryer ebryer@spots.ab.ca Jonathan Cameron jic23@cam.ac.uk Bryan Christianson bryan@whatroute.net Juliusz Chroboczek jch@pps.jussieu.fr Paul Donald newtwen+gitlab@gmail.com Dan Drown dan-ntp@drown.org Kamil Dudka kdudka@redhat.com Christian Ehrhardt christian.ehrhardt@canonical.com Paul Elliott pelliott@io.com Robert Fairley rfairley@redhat.com Ahmad Fatoum a.fatoum@pengutronix.de Andreas Fenkart extern-afe@mission-embedded.com Stefan R. Filipek srfilipek@gmail.com Andy Fiddaman illumos@fiddaman.net Mike Fleetwood mike@rockover.demon.co.uk Rob Gill rrobgill@protonmail.com Alexander Gretencord arutha@gmx.de Andrew Griffiths agriffit@redhat.com Walter Haidinger walter.haidinger@gmx.at Juergen Hannken-Illjes hannken@eis.cs.tu-bs.de John Hasler john@dhh.gt.org Tjalling Hattink t.hattink@fugro.nl Liam Hatton me@liamhatton.com Holger Hoffstätte holger@applied-asynchrony.com Jachym Holecek jakym@volny.cz Håkan Johansson f96hajo@chalmers.se Jim Knoble jmknoble@pobox.com Antti Jrvinen costello@iki.fi Uwe Kleine-König u.kleine-koenig@pengutronix.de Eric Lammerts eric@lammerts.org Stefan Lucke stefan@lucke.in-berlin.de Victor Lum viclum@vanu.com Kevin Lyda kevin@ie.suberic.net Paul Menzel paulepanter@users.sourceforge.net Vladimir Michl vladimir.michl@seznam.cz Victor Moroz vim@prv.adlum.ru Kalle Olavi Niemitalo tosi@stekt.oulu.fi Patrick Oppenlander patrick.oppenlander@gmail.com Frank Otto sandwichmacher@web.de Denny Page dennypage@me.com Rupesh Patel rupatel@redhat.com Chris Perl cperl@janestreet.com Gautier PHILIPPON gautier.philippon@ensimag.grenoble-inp.fr Andreas Piesk apiesk@virbus.de Shachar Raindel shacharr@google.com Mike Ryan msr@hsilop.net Baruch Siach baruch@tkos.co.il Josef 'Jeff' Sipek jeffpc@josefsipek.net Foster Snowhill forst@forstwoof.ru Andreas Steinmetz ast@domdv.de NAKAMURA Takumi takumi@ps.sakura.ne.jp Timo Teras timo.teras@iki.fi Bill Unruh unruh@physics.ubc.ca Luke Valenta lvalenta@cloudflare.com Stephen Wadeley swadeley@redhat.com Bernhard Weiss lisnablagh@web.de Wolfgang Weisselberg weissel@netcologne.de Bernhard M. Wiedemann bwiedemann@suse.de Joachim Wiedorn ad_debian@joonet.de Ralf Wildenhues Ralf.Wildenhues@gmx.de Ulrich Windl ulrich.windl@rz.uni-regensburg.de Michael Witten mfwitten@gmail.com Doug Woodward dougw@whistler.com Thomas Zajic zlatko@zlatko.fdns.net

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