CHRONYD(8) System Administration CHRONYD(8)
NAME
chronyd - chrony background daemon
SYNOPSIS
chronyd [OPTIONS] [configuration commands]
DESCRIPTION
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.
USAGE
chronyd is usually started at boot-time and requires superuser privileges.
If chronyd has been installed to its default location /usr/sbin/chronyd, starting it is simply a matter of
entering the command:
/usr/sbin/chronyd
Information messages and warnings will be logged to syslog.
If no configuration commands are specified on the command line, chronyd will read the commands from the con‐
figuration file (default /etc/chrony.conf).
OPTIONS
A summary of the options supported by chronyd is included below.
-P priority
This option will select the SCHED_FIFO real-time scheduler at the specified priority (which must be
between 0 and 100). This mode is supported only on Linux.
-m This option will lock chronyd into RAM so that it will never be paged out. This mode is only supported
on Linux.
-n When run in this mode, the program will not detach itself from the terminal.
-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. When chronyd was compiled with debugging support, this
option can be used twice to print also debugging messages.
-f conf-file
This option can be used to specify an alternate location for the configuration file (default
/etc/chrony.conf).
-r This option will reload sample histories for each of the servers being used. These histories are cre‐
ated 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
rtcfile directive in the documentation supplied with the distribution.
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 (RTC). 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 deter‐
mine accurate statistics for the difference between the RTC and system clock last time the computer was
on.
If chronyd doesn't support the RTC on your computer or there is no RTC installed, the system clock will
be set with this option forward to the time of the last modification of the drift file (specified by
the driftfile directive) to restore the system time at which chronyd was previously stopped.
-u user
This option sets the name of the user to which will chronyd switch to drop root privileges if compiled
with Linux capabilities support (default chrony).
-q When run in this mode, chronyd will set the system clock once and exit. It will not detach from the
terminal.
-Q This option is similar to -q, but it will only print the offset and not correct the clock.
-v This option displays chronyd's version number to the terminal and exits
-4 Resolve hostnames only to IPv4 addresses and create only IPv4 sockets.
-6 Resolve hostnames only to IPv6 addresses and create only IPv6 sockets.
FILES
/etc/chrony.conf
BUGS
To report bugs, please visit http://chrony.tuxfamily.org/
SEE ALSO
chronyd is documented in detail in the documentation supplied with the distribution (chrony.txt and
chrony.texi).
chronyc(1), chrony.conf(5), hwclock(8), ntpd(8)
http://chrony.tuxfamily.org/
AUTHOR
Richard Curnow <[email protected]>
This man-page was written by Jan Schaumann <[email protected]> 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.
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