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 Informational messages, warnings, and errors will be logged to syslog.
23
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. The compiled-in default value is
36 /etc/chrony.conf.
37 -n
39 When run in this mode, the program will not detach itself from the
40 terminal.
41 -d
43 When run in this mode, the program will not detach itself from the
44 terminal, and all messages will be written to the terminal instead
45 of syslog. If chronyd was compiled with enabled support for
46 debugging, this option can be used twice to enable debug messages.
47 -l file
49 This option enables writing of log messages to a file instead of
50 syslog or the terminal.
51 -L level
53 This option specifies the minimum severity level of messages to be
54 written to the log file, syslog, or terminal. The following levels
55 can be specified: 0 (informational), 1 (warning), 2 (non-fatal
56 error), and 3 (fatal error). The default value is 0.
57 -p
59 When run in this mode, chronyd will print the configuration and
60 exit. It will not detach from the terminal. This option can be used
61 to verify the syntax of the configuration and get the whole
62 configuration, even if it is split into multiple files and read by
63 the include or confdir directive.
64 -q
66 When run in this mode, chronyd will set the system clock once and
67 exit. It will not detach from the terminal.
68 -Q
70 This option is similar to the -q option, except it only prints the
71 offset without making any corrections of the clock and it allows
72 chronyd to be started without root privileges.
73 -r
75 This option will try to reload and then delete files containing
76 sample histories for each of the servers and reference clocks being
77 used. The files are expected to be in the directory specified by
78 the dumpdir directive in the configuration file. This option is
79 useful if you want to stop and restart chronyd briefly for any
80 reason, e.g. to install a new version. However, it should be used
81 only on systems where the kernel can maintain clock compensation
82 whilst not under chronyd’s control (i.e. Linux, FreeBSD, NetBSD,
83 Solaris, and macOS 10.13 or later).
84 -R
86 When this option is used, the initstepslew directive and the
87 makestep directive used with a positive limit will be ignored. This
88 option is useful when restarting chronyd and can be used in
89 conjunction with the -r option.
90 -s
92 This option will set the system clock from the computer’s real-time
93 clock (RTC) or to the last modification time of the file specified
94 by the driftfile directive. Real-time clocks are supported only on
95 Linux.
96 If used in conjunction with the -r flag, chronyd will attempt to
98 preserve the old samples after setting the system clock from the
99 RTC. This can be used to allow chronyd to perform long term
100 averaging of the gain or loss rate across system reboots, and is
101 useful for systems with intermittent access to network that are
102 shut down when not in use. For this to work well, it relies on
103 chronyd having been able to determine accurate statistics for the
104 difference between the RTC and system clock last time the computer
105 was on.
106 If the last modification time of the drift file is later than both
108 the current time and the RTC time, the system time will be set to
109 it to restore the time when chronyd was previously stopped. This is
110 useful on computers that have no RTC or the RTC is broken (e.g. it
111 has no battery).
112 -t timeout
114 This option sets a timeout (in seconds) after which chronyd will
115 exit. If the clock is not synchronised, it will exit with a
116 non-zero status. This is useful with the -q or -Q option to shorten
117 the maximum time waiting for measurements, or with the -r option to
118 limit the time when chronyd is running, but still allow it to
119 adjust the frequency of the system clock.
120 -u user
122 This option sets the name of the system user to which chronyd will
123 switch after start in order to drop root privileges. It overrides
124 the user directive. The compiled-in default value is chrony.
125 On Linux, chronyd needs to be compiled with support for the libcap
127 library. On macOS, FreeBSD, NetBSD and Solaris chronyd forks into
128 two processes. The child process retains root privileges, but can
129 only perform a very limited range of privileged system calls on
130 behalf of the parent.
131 -U
133 This option disables a check for root privileges to allow chronyd
134 to be started under a non-root user, assuming the process will have
135 all capabilities (e.g. provided by the service manager) and access
136 to all files, directories, and devices, needed to operate correctly
137 in the specified configuration. Note that different capabilities
138 might be needed with different configurations and different Linux
139 kernel versions. Starting chronyd under a non-root user is not
140 recommended when the configuration is not known, or at least
141 limited to specific directives.
142 -F level
144 This option configures system call filters loaded by chronyd
145 processes if it was compiled with support for the Linux secure
146 computing (seccomp) facility. Three levels are defined: 0, 1, 2.
147 The filters are disabled at level 0. At levels 1 and 2, chronyd
148 will be killed if it makes a system call which is blocked by the
149 filters. The level can be specified as a negative number to trigger
150 the SIGSYS signal instead of SIGKILL, which can be useful for
151 debugging. The default value is 0.
152 At level 1, the filters allow only selected system calls that are
154 normally expected to be made by chronyd. Other system calls are
155 blocked. This level is recommended only if it is known to work on
156 the version of the system where chrony is installed. The filters
157 need to allow also system calls made by libraries that chronyd is
158 using (e.g. libc), but different versions or implementations of the
159 libraries might make different system calls. If the filters are
160 missing a system call, chronyd could be killed even in normal
161 operation.
162 At level 2, the filters block only a small number of specific
164 system calls (e.g. fork and exec). This approach should avoid false
165 positives, but the protection of the system against a compromised
166 chronyd process is much more limited.
167 The filters cannot be enabled with the mailonchange directive.
169 -P priority
171 On Linux, this option will select the SCHED_FIFO real-time
172 scheduler at the specified priority (which must be between 0 and
173 100). On macOS, this option must have either a value of 0 to
174 disable the thread time constraint policy or 1 for the policy to be
175 enabled. Other systems do not support this option. The default
176 value is 0.
177 -m
179 This option will lock chronyd into RAM so that it will never be
180 paged out. This mode is only supported on Linux.
181 -x
183 This option disables the control of the system clock. chronyd will
184 not try to make any adjustments of the clock. It will assume the
185 clock is free running and still track its offset and frequency
186 relative to the estimated true time. This option allows chronyd to
187 be started without the capability to adjust or set the system clock
188 (e.g. in some containers) to operate as an NTP server.
189 -v, --version
191 With this option chronyd will print version number to the terminal
192 and exit.
193 -h, --help
195 With this option chronyd will print a help message to the terminal
196 and exit.
197
199 /etc/chrony.conf
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202 chronyc(1), chrony.conf(5)
203
205 For instructions on how to report bugs, please visit
206 https://chrony.tuxfamily.org/.
207
209 chrony was written by Richard Curnow, Miroslav Lichvar, and others.
210chrony 4.1 2021-05-12 CHRONYD(8)