CentOS 7.0 - man page for chrony (centos section 1)
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CHRONY(1) User's Manual CHRONY(1)
chrony - programs for keeping computer clocks accurate
chrony is a pair of programs for keeping computer clocks accurate. chronyd is a back-
ground (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.
chronyc is a command-line interface program which can be used to monitor chronyd's perfor-
mance 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 sev-
eral 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, refer-
ence 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 Inter-
net 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 sys-
tem 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.
Richard Curnow <firstname.lastname@example.org>
This man-page was written by Jan Schaumann <email@example.com> as part of "The Miss-
ing Man Pages Project". Please see http://www.netmeister.org/misc/m2p2/index.html for
The complete chrony documentation is supplied in texinfo format.
chrony @VERSION@ @MAN_DATE@ CHRONY(1)
All times are GMT -4. The time now is 07:55 PM.