chronyd - chrony background daemon

chronyd [OPTIONS]

chrony is a pair of programs for maintaining the accuracy of computer clocks. chronyd is a background daemon program that can be started at boot time.

chronyd 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 chronyc). In either case, chronyd determines the rate at which the computer gains or loses time, and compensates for this.

chronyd is usually started at boot-time and requires superuser priviliges.

If chronyd has been installed to its default location /usr/local/sbin/chronyd, starting it is simply a matter of entering the command:

/usr/local/sbin/chronyd

Information messages and warnings will be logged to syslog.

A summary of the options supported by chronyd is included below.

-d

When run in this mode, the program will not detach itself from the terminal, and all messages will be sent to the terminal instead of to syslog.

-f conf-file

This option can be used to specify an alternate location for the configuration file (default /etc/chrony/chrony.conf).

-r

This option will reload sample histories for each of the servers being used. These histories are created by using the dump command in chronyc, or by setting the dumponexit directive in the configuration file. This option is useful if you want to stop and restart chronyd briefly for any reason, e.g. to install a new version. However, it only makes sense on systems where the kernel can maintain clock compensation whilst not under chronyd's control. The only version where this happens so far is Linux. On systems where this is not the case, e.g. Solaris and SunOS the option should not be used.

-s

This option will set the system clock from the computer's real-time clock. This is analogous to supplying the -s flag to the /sbin/clock program during the Linux boot sequence.

Support for real-time clocks is limited at present - the criteria are described in the section on the rtcfile directive in the documentation supplied with the distribution.

If chronyd cannot support the real time clock on your computer, this option cannot be used and a warning message will be logged to the syslog.

If used in conjunction with the -r flag, chronyd will attempt to preserve the old samples after setting the system clock from the real time clock. This can be used to allow chronyd to perform long term averaging of the gain or loss rate across system reboots, and is useful for dial-up systems that are shut down when not in use. For this to work well, it relies on chronyd having been able to determine accurate statistics for the difference between the real time clock and system clock last time the computer was on.

-v

This option displays chronyd's version number to the terminal and exits

/etc/chrony/chrony.conf

Version 1.17

To report bugs, please contact the author and/or visit http://chrony.sunsite.dk/

chronyd is documented in detail in the documentation supplied with the distribution (chrony.txt and chrony.texi) and is also available from http://go.to/chrony

chrony(1), chronyc(1), chrony.conf(5), clock(8), xntpd(8), ntpd(8)

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.