This is the README for chrony.

What is chrony?

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

chronyd is a (background) daemon program that can be started at boot time. This does most of the work.

chronyc is a command-line interface program which can be used to monitor chronyd's performance and to change various operating parateters whilst it is running.

chronyd's main function is to obtain measurements of the true (UTC) time from one of several sources, and correct the system clock accordingly. It also works out the rate at which the system clock gains or loses time and uses this information to keep it accurate between measurements from the reference.

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.

In addition, the Linux 2.0.x (for x >= 32), 2.2.x and 2.3.x versions can monitor the system's real time clock performance, so the system can maintain accurate time even across reboots.

Typical accuracies available between 2 machines are

On an ethernet LAN : 100-200 microseconds, often much better On a V32bis dial-up modem connection : 10's of milliseconds (from one session to the next)

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

What will chrony run on?

Chrony can be successfully built and run on

Linux v1.2.13, v2.0.x, 2.1.x (partially), 2.2.x, 2.3.x, 2.4.x (i386). Real time clock support is limited to 2.0.32 onwards and to 2.2, 2.3 and 2.4 series only. PowerPC is also known to be supported.
Solaris 2.5/2.5.1/2.6/2.7/2.8 (various platforms)
SunOS 4.1.4 (Sparc 2 and Sparc 20)
BSD/386 v1.1 has been reported to work using the SunOS 4.1 driver.
NetBSD.

Any other system will require a porting exercise. You would need to start from one of the existing system-specific drivers and look into the quirks of certain system calls and the kernel on your target system. (This is described in the manual).

How do I set it up?

The file INSTALL gives instructions. On supported systems the compilation process should be automatic.

You will need an ANSI C compiler -- gcc is recommended. Versions 2.7.2/2.7.2.2 are known to work.

The manual (in texinfo and text formats) describes how to set the software up for the less straightforward cases.

What documentation is there?

A manual is supplied in Texinfo format (chrony.texi) and ready-formatted plain text (chrony.txt) in the distribution.

There is also information available on the chrony web pages, accessible through the URL

http://chrony.sunsite.dk/

What can chrony not do?

Compared to the `reference' RFC1305 implementation xntpd, chronyd does not support hardware reference clocks, leap seconds or broadcast modes.

Where are new versions announced?

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

chrony-announce-subscribe@sunsite.dk

These messages will be copied to chrony-users (see below). I also try to announce new versions on Freshmeat (http://freshmeat.net/).

I don't reliably announce via news any more - I don't tend to keep up with news as I haven't enough time.

How can I get support for chrony?
and where can I discuss new features, possible bugs etc?

There are 3 mailing lists relating to chrony. chrony-announce was mentioned above. chrony-users is a users' discussion list, e.g. for general questions and answers about using chrony. chrony-dev is a more technical list, e.g. for discussing how new features should be implemented, exchange of information between developers etc. To subscribe to either of these lists, send an empty message to

chrony-users-subscribe@sunsite.dk
or
chrony-dev-subscribe@sunsite.dk

as applicable.

Note that due to family commitments (a 3 year-old and a 1 year-old), I no longer have the time to give to supporting chrony that I once had. Therefore, the chrony-users list should be your main route for support, rather than mailing me directly. Even if it's me that responds to your question on the list, at least ALL subscribers then benefit from seeing the discussion, rather than me taking up lots of time on supporting people on a one-to-one basis. If you do mail me directly, don't be surprised if I cc: the response to the mailing list.

But how can I contact the author if I need to?

You can email me at <rc@rc0.org.uk>. If that fails, you could try to find me through one of the mailing lists. It would be nice if:

you include the word 'chrony' in the subject line (so my mail reader can sort my mail by topic)
you don't send complete log files, encoded binaries etc, without editing such material down to just the relevant bits - a few tens of lines at most. (My dial-up connection handles large messages rather slowly ...).

Acknowledgements

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

Andrew Bishop <amb@gedanken.demon.co.uk>

Fixes for bugs in logging when in daemon mode Fixes for compiler warnings
Robustness improvements for drift file Improve installation (directory checking etc) Entries in contrib directory
Improvements to 'sources' and 'sourcestats' output from chronyc Improvements to documentation
Investigation of required dosynctodr behaviour for various Solaris versions.

Stephan I. Boettcher <stephan@nevis1.columbia.edu>

Entries in contrib directory

Erik Bryer <ebryer@spots.ab.ca>

Entries in contrib directory

Juliusz Chroboczek <jch@pps.jussieu.fr>

Fix install rule in Makefile if chronyd file is in use.

Paul Elliott <pelliott@io.com>

DNSchrony (in contrib directory), a tool for handling NTP servers with variable IP addresses.

Mike Fleetwood <mike@rockover.demon.co.uk>

Fixes for compiler warnings

Alexander Gretencord <arutha@gmx.de>

Changes to installation directory system to make it easier for package builders.

Walter Haidinger <walter.haidinger@gmx.at>

Providing me with login access to a Linux installation where v1.12 wouldn't compile, so I could develop the fixes for v1.13. Also, for providing the disc space so I can keep an independent backup of the sources.

Juergen Hannken-Illjes <hannken@eis.cs.tu-bs.de>

Port to NetBSD

John Hasler <john@dhh.gt.org>

Changes to support 64 bit machines (i.e. those where sizeof(unsigned long) > 4)
Bug fix to initstepslew directive
Fix to remove potential buffer overrun errors.

Liam Hatton <me@liamhatton.com>

Advice on configuring for Linux on PPC

Jachym Holecek <jakym@volny.cz>

Patch to make Linux real time clock work with devfs

Jim Knoble <jmknoble@pobox.com>

Fixes for compiler warnings

Antti Jrvinen <costello@iki.fi>

Advice on configuring for BSD/386

Victor Moroz <vim@prv.adlum.ru>

Patch to support Linux with HZ!=100

Kalle Olavi Niemitalo <tosi@stekt.oulu.fi>

acquisitionport support