NAME¶
chrony - programs for keeping computer clocks accurate
SYNOPSIS¶
chronyc [
OPTIONS]
chronyd [
OPTIONS]
DESCRIPTION¶
chrony is a pair of programs for keeping computer clocks accurate.
chronyd is a background (daemon) program and
chronyc is a
command-line interface to it. Time reference sources for chronyd can be
RFC1305 NTP servers, human (via keyboard and
chronyc), 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
chronyc) to support computers with
dial-up/intermittent access to the Internet, and it can also act as an
RFC1305-compatible NTP server.
USAGE¶
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 either 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 RFC1305-compatible NTP server and peer.
SEE ALSO¶
chronyc(1), chrony.conf(5), chronyd(8)
http://chrony.tuxfamily.org/
AUTHOR¶
Richard Curnow <rc@rc0.org.uk>
This man-page was written by Jan Schaumann <jschauma@netmeister.org> as
part of "The Missing Man Pages Project". Please see
http://www.netmeister.org/misc/m2p2/index.html for details.
The complete chrony documentation is supplied in texinfo format.