1CHRONYD(8) System Administration CHRONYD(8)
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6 chronyd - chrony daemon
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9 chronyd [OPTION]... [DIRECTIVE]...
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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.
17 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.
21 Information messages and warnings will be logged to syslog.
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25 -4
26 With this option hostnames will be resolved only to IPv4 addresses
27 and only IPv4 sockets will be created.
28 -6
30 With this option hostnames will be resolved only to IPv6 addresses
31 and only IPv6 sockets will be created.
32 -f file
34 This option can be used to specify an alternate location for the
35 configuration file (default /etc/chrony.conf).
36 -n
38 When run in this mode, the program will not detach itself from the
39 terminal.
40 -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.
46 -l file
48 This option specifies a file which should be used for logging
49 instead of syslog or terminal.
50 -q
52 When run in this mode, chronyd will set the system clock once and
53 exit. It will not detach from the terminal.
54 -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.
59 -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).
71 -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.
77 -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.
83 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.
93 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).
99 -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.
107 -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).
112 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.
118 -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 SIGSYS signal is thrown instead and
124 in level 0 the filter is disabled (default 0).
125 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 -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.
140 -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.
144 -x
146 This option disables the control of the system clock. chronyd will
147 not try to make any adjustments of the clock. It will assume the
148 clock is free running and still track its offset and frequency
149 relative to the estimated true time. This option allows chronyd to
150 run without the capability to adjust or set the system clock (e.g.
151 in some containers) in order to operate as an NTP server. It is not
152 recommended to run chronyd (with or without -x) when another
153 process is controlling the system clock.
154 -v
156 With this option chronyd will print version number to the terminal
157 and exit.
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160 /etc/chrony.conf
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163 chronyc(1), chrony.conf(5)
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166 For instructions on how to report bugs, please visit <https://
167 chrony.tuxfamily.org/>.
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170 chrony was written by Richard Curnow, Miroslav Lichvar, and others.
171chrony 3.3 2018-04-04 CHRONYD(8)