.TH CHRONY 1 "August 10, 2001" chrony "User's Manual"
chrony \- programs for keeping computer clocks accurate
\fBchrony\fR is a pair of programs for keeping computer clocks accurate.
\fIchronyd\fR is a background (daemon) program and \fIchronyc\fR is a
command-line interface to it. Time reference sources for chronyd can be
RFC1305 NTP servers, human (via keyboard and \fIchronyc\fR), or the computer's
real-time clock at boot time (Linux only). chronyd can determine the rate at
which the computer gains or loses time and compensate for it while no external
reference is present. Its use of NTP servers can be switched on and off
(through \fIchronyc\fR) to support computers with dial-up/intermittent access
to the Internet, and it can also act as an RFC1305-compatible NTP server.
\fIchronyc\fR is a command-line interface program which can be used to
monitor \fIchronyd\fR's performance and to change various operating
parateters whilst it is running.
\fIchronyd\fR'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 \fIchronyc\fR).
The main source of information about the Network Time Protocol is
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, for Linux 2.0.x (for x >= 32) or 2.2 onwards, chronyd 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)
\fIchronyd\fR can also operate as an RFC1305-compatible NTP server and peer.
.SH "SEE ALSO"
Richard Curnow <email@example.com>
This man-page was written by Jan Schaumann <firstname.lastname@example.org> as part
of "The Missing Man Pages Project". Please see
\fIhttp://www.netmeister.org/misc/m2p2/index.html\fR for details.