161 lines
6.1 KiB
Groff
161 lines
6.1 KiB
Groff
.TH CHRONYD 8 "@MAN_DATE@" "chrony @VERSION@" "System Administration"
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.SH NAME
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chronyd \- chrony background daemon
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.SH SYNOPSIS
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.B chronyd
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[\fIOPTIONS\fR] [\fIconfiguration commands\fR]
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.SH DESCRIPTION
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\fIchrony\fR is a pair of programs for maintaining the accuracy of computer
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clocks. \fBchronyd\fR is a background daemon program that can be started at boot
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time.
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\fBchronyd\fR is a daemon which runs in background on the
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system. It obtains measurements (e.g. via the network) of the
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system's offset relative to other systems, and adjusts the system
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time accordingly. For isolated systems, the user can periodically
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enter the correct time by hand (using \fIchronyc\fR). In either case,
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\fBchronyd\fR determines the rate at which the computer
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gains or loses time, and compensates for this.
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.SH USAGE
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\fBchronyd\fR is usually started at boot-time and requires superuser
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privileges.
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If \fBchronyd\fR has been installed to its default location
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\fI@SBINDIR@/chronyd\fR, starting it is simply a matter of entering the
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command:
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\fI@SBINDIR@/chronyd\fR
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Information messages and warnings will be logged to syslog.
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If no configuration commands are specified on the command line,
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\fBchronyd\fR will read the commands from the configuration file
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(default \fI@SYSCONFDIR@/chrony.conf\fR).
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.SH OPTIONS
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A summary of the options supported by \fBchronyd\fR is included below.
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.TP
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\fB\-P\fR \fIpriority\fR
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On Linux, this option will select the SCHED_FIFO real-time scheduler at the
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specified priority (which must be between 0 and 100). On Mac OS X, this
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option must have either a value of 0 (the default) to disable the thread
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time constraint policy or 1 for the policy to be enabled. Other systems do not
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support this option.
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.TP
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.B \-m
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This option will lock chronyd into RAM so that it will never be paged out.
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This mode is only supported on Linux.
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.TP
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.B \-n
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When run in this mode, the program will not detach itself from the
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terminal.
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.TP
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.B \-d
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When run in this mode, the program will not detach itself from the
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terminal, and all messages will be sent to the terminal instead of
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to syslog. When \fBchronyd\fR was compiled with debugging support,
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this option can be used twice to print also debugging messages.
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.TP
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\fB\-f\fR \fIconf-file\fR
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This option can be used to specify an alternate location for the
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configuration file (default \fI@SYSCONFDIR@/chrony.conf\fR).
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.TP
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.B \-r
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This option will reload sample histories for each of the servers being used.
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These histories are created by using the \fIdump\fR command in \fIchronyc\fR,
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or by setting the \fIdumponexit\fR directive in the configuration file. This
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option is useful if you want to stop and restart \fBchronyd\fR briefly for any
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reason, e.g. to install a new version. However, it should be used only on
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systems where the kernel can maintain clock compensation whilst not under
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\fBchronyd\fR's control (i.e. Linux, FreeBSD, NetBSD and Solaris).
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.TP
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.B \-R
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When this option is used, the \fIinitstepslew\fR directive and the
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\fImakestep\fR directive used with a positive limit will be ignored. This
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option is useful when restarting \fBchronyd\fR and can be used in conjunction
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with the \fB-r\fR option.
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.TP
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.B \-s
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This option will set the system clock from the computer's real-time
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clock. This is analogous to supplying the \fI-s\fR flag to the
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\fI/sbin/hwclock\fR program during the Linux boot sequence.
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Support for real-time clocks is limited at present - the criteria
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are described in the section on the \fIrtcfile\fR directive in the
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documentation supplied with the distribution.
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If used in conjunction with the \fB-r\fR flag, \fBchronyd\fR will attempt
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to preserve the old samples after setting the system clock from
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the real time clock (RTC). This can be used to allow \fBchronyd\fR to
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perform long term averaging of the gain or loss rate across system
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reboots, and is useful for dial-up systems that are shut down when
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not in use. For this to work well, it relies on \fBchronyd\fR having
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been able to determine accurate statistics for the difference
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between the RTC and system clock last time the computer was on.
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If \fBchronyd\fR doesn't support the RTC on your computer or there is no RTC
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installed, the system clock will be set with this option forward to the time of
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the last modification of the drift file (specified by the \fIdriftfile\fR
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directive) to restore the system time at which \fBchronyd\fR was previously
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stopped.
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.TP
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\fB\-u\fR \fIuser\fR
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This option sets the name of the system user to which \fBchronyd\fR will switch
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after start in order to drop root privileges. It overrides the \fBuser\fR
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directive (default \fB@DEFAULT_USER@\fR). It may be set to a non-root user
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only when \fBchronyd\fR is compiled with support for Linux capabilities
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(libcap) or on NetBSD with the \fB/dev/clockctl\fR device.
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.TP
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\fB\-F\fR \fIlevel\fR
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This option configures a system call filter when \fBchronyd\fR is compiled with
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support for the Linux secure computing (seccomp) facility. In level 1 the
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process is killed when a forbidden system call is made, in level -1 the SYSSIG
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signal is thrown instead and in level 0 the filter is disabled (default 0).
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.TP
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.B \-q
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When run in this mode, chronyd will set the system clock once
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and exit. It will not detach from the terminal.
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.TP
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.B \-Q
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This option is similar to \fB\-q\fR, but it will only print the offset and
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not correct the clock.
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.TP
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.B \-v
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This option displays \fBchronyd\fR's version number to the terminal and exits
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.TP
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.B \-4
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Resolve hostnames only to IPv4 addresses and create only IPv4 sockets.
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.TP
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.B \-6
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Resolve hostnames only to IPv6 addresses and create only IPv6 sockets.
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.SH FILES
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\fI@SYSCONFDIR@/chrony.conf\fR
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.SH BUGS
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To report bugs, please visit \fIhttp://chrony.tuxfamily.org/\fR
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.SH "SEE ALSO"
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\fBchronyd\fR is documented in detail in the documentation supplied with the
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distribution (\fIchrony.txt\fR and \fIchrony.texi\fR).
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.BR chronyc(1),
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.BR chrony.conf(5),
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.BR hwclock(8),
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.BR ntpd(8)
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.I http://chrony.tuxfamily.org/
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.SH AUTHOR
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Richard Curnow <rc@rc0.org.uk>
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This man-page was written by Jan Schaumann <jschauma@netmeister.org> as part
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of "The Missing Man Pages Project". Please see
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\fIhttp://www.netmeister.org/misc/m2p2/index.html\fR for details.
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The complete chrony documentation is supplied in texinfo format.
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