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. 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).
70 -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.
76 -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.
82 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.
92 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).
98 -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.
106 -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).
111 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.
117 -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 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.
132 -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.
139 -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.
143 -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.
153 -v
155 With this option chronyd will print version number to the terminal
156 and exit.
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159 /etc/chrony.conf
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162 chronyc(1), chrony.conf(5)
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165 For instructions on how to report bugs, please visit <https://
166 chrony.tuxfamily.org/>.
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169 chrony was written by Richard Curnow, Miroslav Lichvar, and others.
170chrony 3.4 2018-09-19 CHRONYD(8)