1CHRONYD(8) System Administration CHRONYD(8)
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6 chronyd - chrony background daemon
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10 chronyd [OPTIONS]
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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 priv‐
28 iliges.
29 If chronyd has been installed to its default location
31 /usr/local/sbin/chronyd, starting it is simply a matter of entering the
32 command:
33 /usr/local/sbin/chronyd
35 Information messages and warnings will be logged to syslog.
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41 A summary of the options supported by chronyd is included below.
42 -P priority
45 This option will select the SCHED_FIFO real-time scheduler at
46 the specified priority (which must be between 0 and 100). This
47 mode is supported only on Linux.
48 -m This option will lock chronyd into RAM so that it will never be
50 paged out. This mode is only supported on Linux.
51 -n When run in this mode, the program will not detach itself from
53 the terminal.
54 -d When run in this mode, the program will not detach itself from
56 the terminal, and all messages will be sent to the terminal
57 instead of to syslog.
58 -f conf-file
60 This option can be used to specify an alternate location for the
61 configuration file (default /etc/chrony.conf).
62 -r This option will reload sample histories for each of the servers
64 being used. These histories are created by using the dump com‐
65 mand in chronyc, or by setting the dumponexit directive in the
66 configuration file. This option is useful if you want to stop
67 and restart chronyd briefly for any reason, e.g. to install a
68 new version. However, it only makes sense on systems where the
69 kernel can maintain clock compensation whilst not under
70 chronyd's control. The only version where this happens so far
71 is Linux. On systems where this is not the case, e.g. Solaris
72 and SunOS the option should not be used.
73 -s This option will set the system clock from the computer's real-
75 time clock. This is analogous to supplying the -s flag to the
76 /sbin/clock program during the Linux boot sequence.
77 Support for real-time clocks is limited at present - the crite‐
79 ria are described in the section on the rtcfile directive in the
80 documentation supplied with the distribution.
81 If chronyd cannot support the real time clock on your computer,
83 this option cannot be used and a warning message will be logged
84 to the syslog.
85 If used in conjunction with the -r flag, chronyd will attempt to
87 preserve the old samples after setting the system clock from the
88 real time clock. This can be used to allow chronyd to perform
89 long term averaging of the gain or loss rate across system
90 reboots, and is useful for dial-up systems that are shut down
91 when not in use. For this to work well, it relies on chronyd
92 having been able to determine accurate statistics for the dif‐
93 ference between the real time clock and system clock last time
94 the computer was on.
95 -u user
97 When this option is used, chronyd will drop root privileges to
98 the specified user. So far, it works only on Linux when com‐
99 piled with capabilities support.
100 -v This option displays chronyd's version number to the terminal
102 and exits
103 -4 Resolve hostnames only to IPv4 addresses.
105 -6 Resolve hostnames only to IPv6 addresses.
107
110 /etc/chrony.conf
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114 Version 1.25
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118 To report bugs, please visit http://chrony.tuxfamily.org/
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122 chronyd is documented in detail in the documentation supplied with the
123 distribution (chrony.txt and chrony.texi) and is also available from
124 http://go.to/chrony
125 chrony(1), chronyc(1), chrony.conf(5), clock(8), xntpd(8), ntpd(8)
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130 Richard Curnow <rc@rc0.org.uk>
131 This man-page was written by Jan Schaumann <jschauma@netmeister.org> as
133 part of "The Missing Man Pages Project". Please see http://www.net‐
134 meister.org/misc/m2p2/index.html for details.
135 The complete chrony documentation is supplied in texinfo format.
137chrony May 02, 2011 CHRONYD(8)