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
-parameters 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 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.
-
+chrony is a versatile implementation of the Network Time Protocol (NTP).
+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.
+
+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 on a LAN is in tens, or a few
+hundreds, of microseconds; over the Internet, accuracy is typically
+within a few milliseconds. With a good hardware reference clock
+sub-microsecond accuracy is 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 and Solaris. Closely
-related systems may work too. Any other system will likely 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.
+The software is known to work on Linux, FreeBSD, NetBSD and Solaris.
+Closely related systems may work too. Any other system will likely
+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.
How do I set it up?
===================
as applicable.
+License
+=======
+
+chrony is distributed under the GNU General Public License version 2.
+
Author
======
@c {{{ S:Overview
@node Overview
@section Overview
-Chrony is a software package for maintaining the accuracy of computer
-system clocks. It consists of a pair of programs :
-
-@itemize @bullet
-@item @code{chronyd}. This is a daemon which runs in background on the
-system. It obtains measurements (e.g. via the network) of the system's
-offset relative to other systems, and adjusts the system time
-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
-to other computers. A typical set-up is to run @code{chronyd} on a gateway
-computer that has a dial-up link to the Internet, and use it to serve time to
-computers on a private LAN sitting behind the gateway. The IP addresses that
-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
-monitoring program. An administrator can use this to fine-tune various
-parameters within the daemon, add or delete servers etc whilst the
-daemon is running.
+chrony is a versatile implementation of the Network Time Protocol (NTP).
+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.
+
+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 on a LAN is in tens, or a few
+hundreds, of microseconds; over the Internet, accuracy is typically
+within a few milliseconds. With a good hardware reference clock
+sub-microsecond accuracy is possible.
+
+Two programs are included in chrony, @code{chronyd} is a daemon that can
+be started at boot time and @code{chronyc} is a command-line interface
+program which can be used to monitor @code{chronyd}'s performance and to
+change various operating parameters whilst it is running.
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
running on.
-@end itemize
@c }}}
@c {{{ S:Acknowledgments
@node Acknowledgements
projects / thirdparty / chrony.git / commitdiff
