1CHRONYD(8) System Administration CHRONYD(8)
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6 chronyd - chrony background daemon
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10 chronyd [OPTIONS] [configuration commands]
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14 chrony is a pair of programs for maintaining the accuracy of computer
15 clocks. chronyd is a background daemon program that can be started at
16 boot time.
17 chronyd is a daemon which runs in background on the system. It obtains
19 measurements (e.g. via the network) of the system's offset relative to
20 other systems, and adjusts the system time accordingly. For isolated
21 systems, the user can periodically enter the correct time by hand
22 (using chronyc). In either case, chronyd determines the rate at which
23 the computer gains or loses time, and compensates for this.
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27 chronyd is usually started at boot-time and requires superuser privi‐
28 leges.
29 If chronyd has been installed to its default location
31 /usr/sbin/chronyd, starting it is simply a matter of entering the com‐
32 mand:
33 /usr/sbin/chronyd
35 Information messages and warnings will be logged to syslog.
37 If no configuration commands are specified on the command line, chronyd
39 will read the commands from the configuration file (default
40 /etc/chrony.conf).
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44 A summary of the options supported by chronyd is included below.
45 -P priority
48 This option will select the SCHED_FIFO real-time scheduler at
49 the specified priority (which must be between 0 and 100). This
50 mode is supported only on Linux.
51 -m This option will lock chronyd into RAM so that it will never be
53 paged out. This mode is only supported on Linux.
54 -n When run in this mode, the program will not detach itself from
56 the terminal.
57 -d When run in this mode, the program will not detach itself from
59 the terminal, and all messages will be sent to the terminal
60 instead of to syslog. When chronyd was compiled with debugging
61 support, this option can be used twice to print also debugging
62 messages.
63 -f conf-file
65 This option can be used to specify an alternate location for the
66 configuration file (default /etc/chrony.conf).
67 -r This option will reload sample histories for each of the servers
69 being used. These histories are created by using the dump com‐
70 mand in chronyc, or by setting the dumponexit directive in the
71 configuration file. This option is useful if you want to stop
72 and restart chronyd briefly for any reason, e.g. to install a
73 new version. However, it only makes sense on systems where the
74 kernel can maintain clock compensation whilst not under
75 chronyd's control. The only version where this happens so far
76 is Linux. On other systems this option should not be used.
77 -R When this option is used, the initstepslew directive and the
79 makestep directive used with a positive limit will be ignored.
80 This option is useful when restarting chronyd and can be used in
81 conjunction with the -r option.
82 -s This option will set the system clock from the computer's real-
84 time clock. This is analogous to supplying the -s flag to the
85 /sbin/hwclock program during the Linux boot sequence.
86 Support for real-time clocks is limited at present - the crite‐
88 ria are described in the section on the rtcfile directive in the
89 documentation supplied with the distribution.
90 If used in conjunction with the -r flag, chronyd will attempt to
92 preserve the old samples after setting the system clock from the
93 real time clock (RTC). This can be used to allow chronyd to
94 perform long term averaging of the gain or loss rate across sys‐
95 tem reboots, and is useful for dial-up systems that are shut
96 down when not in use. For this to work well, it relies on
97 chronyd having been able to determine accurate statistics for
98 the difference between the RTC and system clock last time the
99 computer was on.
100 If chronyd doesn't support the RTC on your computer or there is
102 no RTC installed, the system clock will be set with this option
103 forward to the time of the last modification of the drift file
104 (specified by the driftfile directive) to restore the system
105 time at which chronyd was previously stopped.
106 -u user
108 This option sets the name of the user to which will chronyd
109 switch to drop root privileges if compiled with Linux capabili‐
110 ties support (default chrony).
111 -q When run in this mode, chronyd will set the system clock once
113 and exit. It will not detach from the terminal.
114 -Q This option is similar to -q, but it will only print the offset
116 and not correct the clock.
117 -v This option displays chronyd's version number to the terminal
119 and exits
120 -4 Resolve hostnames only to IPv4 addresses and create only IPv4
122 sockets.
123 -6 Resolve hostnames only to IPv6 addresses and create only IPv6
125 sockets.
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129 /etc/chrony.conf
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133 To report bugs, please visit http://chrony.tuxfamily.org/
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137 chronyd is documented in detail in the documentation supplied with the
138 distribution (chrony.txt and chrony.texi).
139 chronyc(1), chrony.conf(5), hwclock(8), ntpd(8)
141 http://chrony.tuxfamily.org/
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146 Richard Curnow <rc@rc0.org.uk>
147 This man-page was written by Jan Schaumann <jschauma@netmeister.org> as
149 part of "The Missing Man Pages Project". Please see http://www.net‐
150 meister.org/misc/m2p2/index.html for details.
151 The complete chrony documentation is supplied in texinfo format.
153chrony 2.1.1 June 2015 CHRONYD(8)