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 configuration file (default /etc/chrony.conf).

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

-P priority
    On Linux, this option will select the SCHED_FIFO real-time scheduler at the specified priority (which must be between 0 and 100). On Mac OS X, this option must have either a value of 0 (the default) to disable the thread time constraint policy or 1 for the policy to be enabled. Other systems do not support this option.

-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 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 should be used only on systems where the kernel can maintain clock compensation whilst not under chronyd's control (i.e. Linux, FreeBSD, NetBSD and Solaris).

-R  When this option is used, the initstepslew directive and the makestep directive used with a positive limit will be ignored. This option is useful when restarting chronyd and can be used in conjunction with the -r option.

-s  This option will set the system clock from the computer's real-time clock or to the last modification time of the file specified by the driftfile directive. Real-time clocks are supported only on Linux. 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 determine accurate statistics for the difference between the RTC and system clock last time the computer was on. If the last modification time of the drift file is later than the current time and the RTC time, the system time will be set to it to restore the time when chronyd was previously stopped. This is useful on computers that have no RTC or the RTC is broken (e.g. it has no battery).

-u user
    This option sets the name of the system user to which chronyd will switch after start in order to drop root privileges. It overrides the user directive from the configuration file (default root). On Linux, chronyd needs to be compiled with support for the libcap library. On Mac OS X, FreeBSD, NetBSD and Solaris chronyd forks into two processes. The child process retains root privileges, but can only perform a very limited range of privileged system calls on behalf of the parent.

-F level
    This option configures a system call filter when chronyd is compiled with support for the Linux secure computing (seccomp) facility. In level 1 the process is killed when a forbidden system call is made, in level -1 the SYSSIG signal is thrown instead and in level 0 the filter is disabled (default 0). It's recommended to enable the filter only when it's known to work on the version of the system where chrony is installed as the filter needs to allow also system calls made from libraries that chronyd is using (e.g. libc) and different versions or implementations of the libraries may make different system calls. If the filter is missing some system call, chronyd could be killed even in normal operation.

-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 <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.