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. These histories are created by using the dump command in
64           chronyc, or by setting the dumponexit directive in the
65           configuration file. This option is useful if you want to stop and
66           restart chronyd briefly for any reason, e.g. to install a new
67           version. However, it should be used only on systems where the
68           kernel can maintain clock compensation whilst not under chronyd’s
69           control (i.e. Linux, FreeBSD, NetBSD, Solaris, and macOS 10.13 or
70           later).
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72       -R
73           When this option is used, the initstepslew directive and the
74           makestep directive used with a positive limit will be ignored. This
75           option is useful when restarting chronyd and can be used in
76           conjunction with the -r option.
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78       -s
79           This option will set the system clock from the computer’s real-time
80           clock (RTC) or to the last modification time of the file specified
81           by the driftfile directive. Real-time clocks are supported only on
82           Linux.
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84           If used in conjunction with the -r flag, chronyd will attempt to
85           preserve the old samples after setting the system clock from the
86           RTC. This can be used to allow chronyd to perform long term
87           averaging of the gain or loss rate across system reboots, and is
88           useful for systems with intermittent access to network that are
89           shut down when not in use. For this to work well, it relies on
90           chronyd having been able to determine accurate statistics for the
91           difference between the RTC and system clock last time the computer
92           was on.
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94           If the last modification time of the drift file is later than both
95           the current time and the RTC time, the system time will be set to
96           it to restore the time when chronyd was previously stopped. This is
97           useful on computers that have no RTC or the RTC is broken (e.g. it
98           has no battery).
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100       -t timeout
101           This option sets a timeout (in seconds) after which chronyd will
102           exit. If the clock is not synchronised, it will exit with a
103           non-zero status. This is useful with the -q or -Q option to shorten
104           the maximum time waiting for measurements, or with the -r option to
105           limit the time when chronyd is running, but still allow it to
106           adjust the frequency of the system clock.
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108       -u user
109           This option sets the name of the system user to which chronyd will
110           switch after start in order to drop root privileges. It overrides
111           the user directive (default chrony).
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113           On Linux, chronyd needs to be compiled with support for the libcap
114           library. On macOS, FreeBSD, NetBSD and Solaris chronyd forks into
115           two processes. The child process retains root privileges, but can
116           only perform a very limited range of privileged system calls on
117           behalf of the parent.
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119       -F level
120           This option configures a system call filter when chronyd is
121           compiled with support for the Linux secure computing (seccomp)
122           facility. In level 1 the process is killed when a forbidden system
123           call is made, in level -1 the SYSSIG signal is thrown instead and
124           in level 0 the filter is disabled (default 0).
125
126           It’s recommended to enable the filter only when it’s known to work
127           on the version of the system where chrony is installed as the
128           filter needs to allow also system calls made from libraries that
129           chronyd is using (e.g. libc) and different versions or
130           implementations of the libraries may make different system calls.
131           If the filter is missing some system call, chronyd could be killed
132           even in normal operation.
133
134       -P priority
135           On Linux, this option will select the SCHED_FIFO real-time
136           scheduler at the specified priority (which must be between 0 and
137           100). On macOS, this option must have either a value of 0 (the
138           default) to disable the thread time constraint policy or 1 for the
139           policy to be enabled. Other systems do not support this option.
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141       -m
142           This option will lock chronyd into RAM so that it will never be
143           paged out. This mode is only supported on Linux.
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145       -x
146           This option disables the control of the system clock. chronyd will
147           not make any adjustments of the clock, but it will still track its
148           offset and frequency relative to the estimated true time, and be
149           able to operate as an NTP server. This allows chronyd to run
150           without the capability to adjust or set the system clock (e.g. in
151           some containers).
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153       -v
154           With this option chronyd will print version number to the terminal
155           and exit.
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FILES

158       /etc/chrony.conf
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SEE ALSO

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

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

168       chrony was written by Richard Curnow, Miroslav Lichvar, and others.
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172chrony 3.2                        2017-09-15                        CHRONYD(8)
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