diff --git a/README b/README index 802e3bb..e7993a5 100644 --- a/README +++ b/README @@ -3,56 +3,35 @@ This is the README for chrony. What is chrony? =============== -Chrony is a pair of programs for maintaining the accuracy of computer -clocks. +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. -chronyd is a (background) daemon program that can be started at boot -time. This does most of the work. +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. -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. +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? =================== @@ -105,6 +84,11 @@ chrony-dev-request@chrony.tuxfamily.org as applicable. +License +======= + +chrony is distributed under the GNU General Public License version 2. + Author ====== diff --git a/chrony.texi.in b/chrony.texi.in index a44466a..513e208 100644 --- a/chrony.texi.in +++ b/chrony.texi.in @@ -56,34 +56,30 @@ Copyright @copyright{} 2009-2014 Miroslav Lichvar @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 : +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. -@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. +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. -@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. +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. -@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. +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