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doc: update chrony description

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Miroslav Lichvar 2015-04-24 10:46:52 +02:00
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README
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@ -3,56 +3,35 @@ This is the README for chrony.
What is chrony? What is chrony?
=============== ===============
Chrony is a pair of programs for maintaining the accuracy of computer chrony is a versatile implementation of the Network Time Protocol (NTP).
clocks. It can synchronize 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.
chronyd is a (background) daemon program that can be started at boot It is designed to perform well in a wide range of conditions, including
time. This does most of the work. 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.
chronyc is a command-line interface program which can be used to Typical accuracy between two machines on a LAN is in tens, or a few
monitor chronyd's performance and to change various operating hundreds, of microseconds; over the Internet, accuracy is typically
parameters whilst it is running. within a few milliseconds. With a good hardware reference clock
sub-microsecond accuracy is possible.
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 Network Time Protocol (NTP)
servers, reference clocks, or wristwatch-and-keyboard (via chronyc).
The main source of information about the Network Time Protocol is
http://www.ntp.org.
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 or laptops. Of course, it
will work well on computers with permanent connections too.
In addition, on Linux it 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)
With a good reference clock the accuracy can reach one microsecond.
chronyd can also operate as an NTPv4 (RFC 5905) server, peer and broadcast
server.
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? What will chrony run on?
======================== ========================
The software is known to work on Linux, FreeBSD, NetBSD and Solaris. Closely The software is known to work on Linux, FreeBSD, NetBSD and Solaris.
related systems may work too. Any other system will likely require a porting Closely related systems may work too. Any other system will likely
exercise. You would need to start from one of the existing system-specific require a porting exercise. You would need to start from one of the
drivers and look into the quirks of certain system calls and the kernel on your existing system-specific drivers and look into the quirks of certain
target system. system calls and the kernel on your target system.
How do I set it up? How do I set it up?
=================== ===================
@ -105,6 +84,11 @@ chrony-dev-request@chrony.tuxfamily.org
as applicable. as applicable.
License
=======
chrony is distributed under the GNU General Public License version 2.
Author Author
====== ======

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chrony.texi.in
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@ -56,34 +56,30 @@ Copyright @copyright{} 2009-2014 Miroslav Lichvar
@c {{{ S:Overview @c {{{ S:Overview
@node Overview @node Overview
@section Overview @section Overview
Chrony is a software package for maintaining the accuracy of computer chrony is a versatile implementation of the Network Time Protocol (NTP).
system clocks. It consists of a pair of programs : It can synchronize 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.
@itemize @bullet It is designed to perform well in a wide range of conditions, including
@item @code{chronyd}. This is a daemon which runs in background on the intermittent network connections, heavily congested networks, changing
system. It obtains measurements (e.g. via the network) of the system's temperatures (ordinary computer clocks are sensitive to temperature),
offset relative to other systems, and adjusts the system time and systems that do not run continuosly, or run on a virtual machine.
accordingly. For isolated systems, the user can periodically enter the
correct time by hand (using @code{chronyc}). In either case,
@code{chronyd} determines the rate at which the computer gains or loses
time, and compensates for this.
@code{chronyd} can also act as an NTP server, and provide a time-of-day service Typical accuracy between two machines on a LAN is in tens, or a few
to other computers. A typical set-up is to run @code{chronyd} on a gateway hundreds, of microseconds; over the Internet, accuracy is typically
computer that has a dial-up link to the Internet, and use it to serve time to within a few milliseconds. With a good hardware reference clock
computers on a private LAN sitting behind the gateway. The IP addresses that sub-microsecond accuracy is possible.
can act as clients of @code{chronyd} can be tightly controlled. The default is
no client access.
@item @code{chronyc}. This is a command-line driven control and Two programs are included in chrony, @code{chronyd} is a daemon that can
monitoring program. An administrator can use this to fine-tune various be started at boot time and @code{chronyc} is a command-line interface
parameters within the daemon, add or delete servers etc whilst the program which can be used to monitor @code{chronyd}'s performance and to
daemon is running. change various operating parameters whilst it is running.
The IP addresses from which @code{chronyc} clients may connect can be tightly The IP addresses from which @code{chronyc} clients may connect can be tightly
controlled. The default is just the computer that @code{chronyd} itself is controlled. The default is just the computer that @code{chronyd} itself is
running on. running on.
@end itemize
@c }}} @c }}}
@c {{{ S:Acknowledgments @c {{{ S:Acknowledgments
@node Acknowledgements @node Acknowledgements