OPTIONS¶
-4
With this option hostnames will be resolved only to IPv4
addresses and only IPv4 sockets will be created.
-6
With this option hostnames will be resolved only to IPv6
addresses and only IPv6 sockets will be created.
-f file
This option can be used to specify an alternate location
for the configuration file (default /etc/chrony.conf).
-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 written to the terminal instead of
syslog. When chronyd was compiled with debugging support, this option
can be used twice to print also debugging messages.
-l file
This option specifies a file which should be used for
logging instead of syslog or terminal.
-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 the -q option, except it
only prints the offset without making any corrections of the clock and it
allows chronyd to be started without root privileges.
-r
This option will try to reload and then delete files
containing sample histories for each of the servers and reference clocks being
used. The files are expected to be in the directory specified by the
dumpdir 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, Solaris, and
macOS 10.13 or later).
-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 (RTC) 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 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
systems with intermittent access to network 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 both
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).
-t timeout
This option sets a timeout (in seconds) after which
chronyd will exit. If the clock is not synchronised, it will exit with
a non-zero status. This is useful with the -q or -Q option to
shorten the maximum time waiting for measurements, or with the -r
option to limit the time when chronyd is running, but still allow it to
adjust the frequency of the system clock.
-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 (default
chrony).
On Linux, chronyd needs to be compiled with support for the
libcap library. On macOS, 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 SIGSYS 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.
-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 macOS, 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.
-x
This option disables the control of the system clock.
chronyd will not try to make any adjustments of the clock. It will
assume the clock is free running and still track its offset and frequency
relative to the estimated true time. This option allows chronyd to run
without the capability to adjust or set the system clock (e.g. in some
containers) in order to operate as an NTP server. It is not recommended to run
chronyd (with or without -x) when another process is controlling
the system clock.
-v
With this option chronyd will print version number
to the terminal and exit.