CHRONY(1) User's Manual CHRONY(1)NAMEchrony - programs for keeping computer clocks accurate
DESCRIPTIONchrony 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/inter‐
mittent access to the Internet, and it can also act as an RFC1305-com‐
patible NTP server.
chronyc is a command-line interface program which can be used to moni‐
tor 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 accord‐
ingly. It also works out the rate at which the system clock gains or
loses time and uses this information to keep it accurate between mea‐
surements 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 Proto‐
col is http://www.ntp.org.
It is designed so that it can work on computers which only have inter‐
mittent 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 per‐
formance, 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 ses‐
sion 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 ALSOchronyc(1), chrony(1)
Richard Curnow <firstname.lastname@example.org>
This man-page was written by Jan Schaumann <email@example.com> as
part of "The Missing Man Pages Project". Please see http://www.net‐
meister.org/misc/m2p2/index.html for details.
The complete chrony documentation is supplied in texinfo format.
chrony @VERSION@ @MAN_DATE@ CHRONY(1)