1CHRONYD(8)                   System Administration                  CHRONYD(8)
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NAME

6       chronyd - chrony daemon
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SYNOPSIS

9       chronyd [OPTION]... [DIRECTIVE]...
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DESCRIPTION

12       chronyd is a daemon for synchronisation of the system clock. It can
13       synchronise the clock with NTP servers, reference clocks (e.g. a GPS
14       receiver), and manual input using wristwatch and keyboard via chronyc.
15       It can also operate as an NTPv4 (RFC 5905) server and peer to provide a
16       time service to other computers in the network.
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18       If no configuration directives are specified on the command line,
19       chronyd will read them from a configuration file. The compiled-in
20       default location of the file is /etc/chrony.conf.
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22       Information messages and warnings will be logged to syslog.
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OPTIONS

25       -4
26           With this option hostnames will be resolved only to IPv4 addresses
27           and only IPv4 sockets will be created.
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29       -6
30           With this option hostnames will be resolved only to IPv6 addresses
31           and only IPv6 sockets will be created.
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33       -f file
34           This option can be used to specify an alternate location for the
35           configuration file (default /etc/chrony.conf).
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37       -n
38           When run in this mode, the program will not detach itself from the
39           terminal.
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41       -d
42           When run in this mode, the program will not detach itself from the
43           terminal, and all messages will be written to the terminal instead
44           of syslog. When chronyd was compiled with debugging support, this
45           option can be used twice to print also debugging messages.
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47       -l file
48           This option specifies a file which should be used for logging
49           instead of syslog or terminal.
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51       -q
52           When run in this mode, chronyd will set the system clock once and
53           exit. It will not detach from the terminal.
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55       -Q
56           This option is similar to the -q option, except it only prints the
57           offset without making any corrections of the clock and it allows
58           chronyd to be started without root privileges.
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60       -r
61           This option will try to reload and then delete files containing
62           sample histories for each of the servers and reference clocks being
63           used. The files are expected to be in the directory specified by
64           the dumpdir directive in the configuration file. This option is
65           useful if you want to stop and restart chronyd briefly for any
66           reason, e.g. to install a new version. However, it should be used
67           only on systems where the kernel can maintain clock compensation
68           whilst not under chronyd’s control (i.e. Linux, FreeBSD, NetBSD,
69           Solaris, and macOS 10.13 or later).
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71       -R
72           When this option is used, the initstepslew directive and the
73           makestep directive used with a positive limit will be ignored. This
74           option is useful when restarting chronyd and can be used in
75           conjunction with the -r option.
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77       -s
78           This option will set the system clock from the computer’s real-time
79           clock (RTC) or to the last modification time of the file specified
80           by the driftfile directive. Real-time clocks are supported only on
81           Linux.
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83           If used in conjunction with the -r flag, chronyd will attempt to
84           preserve the old samples after setting the system clock from the
85           RTC. This can be used to allow chronyd to perform long term
86           averaging of the gain or loss rate across system reboots, and is
87           useful for systems with intermittent access to network that are
88           shut down when not in use. For this to work well, it relies on
89           chronyd having been able to determine accurate statistics for the
90           difference between the RTC and system clock last time the computer
91           was on.
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93           If the last modification time of the drift file is later than both
94           the current time and the RTC time, the system time will be set to
95           it to restore the time when chronyd was previously stopped. This is
96           useful on computers that have no RTC or the RTC is broken (e.g. it
97           has no battery).
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99       -t timeout
100           This option sets a timeout (in seconds) after which chronyd will
101           exit. If the clock is not synchronised, it will exit with a
102           non-zero status. This is useful with the -q or -Q option to shorten
103           the maximum time waiting for measurements, or with the -r option to
104           limit the time when chronyd is running, but still allow it to
105           adjust the frequency of the system clock.
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107       -u user
108           This option sets the name of the system user to which chronyd will
109           switch after start in order to drop root privileges. It overrides
110           the user directive (default chrony).
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112           On Linux, chronyd needs to be compiled with support for the libcap
113           library. On macOS, FreeBSD, NetBSD and Solaris chronyd forks into
114           two processes. The child process retains root privileges, but can
115           only perform a very limited range of privileged system calls on
116           behalf of the parent.
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118       -F level
119           This option configures a system call filter when chronyd is
120           compiled with support for the Linux secure computing (seccomp)
121           facility. In level 1 the process is killed when a forbidden system
122           call is made, in level -1 the SIGSYS signal is thrown instead and
123           in level 0 the filter is disabled (default 0).
124
125           It’s recommended to enable the filter only when it’s known to work
126           on the version of the system where chrony is installed as the
127           filter needs to allow also system calls made from libraries that
128           chronyd is using (e.g. libc) and different versions or
129           implementations of the libraries may make different system calls.
130           If the filter is missing some system call, chronyd could be killed
131           even in normal operation.
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133       -P priority
134           On Linux, this option will select the SCHED_FIFO real-time
135           scheduler at the specified priority (which must be between 0 and
136           100). On macOS, this option must have either a value of 0 (the
137           default) to disable the thread time constraint policy or 1 for the
138           policy to be enabled. Other systems do not support this option.
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140       -m
141           This option will lock chronyd into RAM so that it will never be
142           paged out. This mode is only supported on Linux.
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144       -x
145           This option disables the control of the system clock. chronyd will
146           not try to make any adjustments of the clock. It will assume the
147           clock is free running and still track its offset and frequency
148           relative to the estimated true time. This option allows chronyd to
149           run without the capability to adjust or set the system clock (e.g.
150           in some containers) in order to operate as an NTP server. It is not
151           recommended to run chronyd (with or without -x) when another
152           process is controlling the system clock.
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154       -v
155           With this option chronyd will print version number to the terminal
156           and exit.
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FILES

159       /etc/chrony.conf
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SEE ALSO

162       chronyc(1), chrony.conf(5)
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BUGS

165       For instructions on how to report bugs, please visit <https://
166       chrony.tuxfamily.org/>.
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AUTHORS

169       chrony was written by Richard Curnow, Miroslav Lichvar, and others.
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173chrony 3.5                        2019-05-10                        CHRONYD(8)
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