doc: update description of local directive
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Miroslav Lichvar
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1 changed files with 53 additions and 22 deletions
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@ -1079,34 +1079,65 @@ This directive, which takes no arguments, specifies that client accesses are
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not to be logged. Normally they are logged, allowing statistics to be reported
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not to be logged. Normally they are logged, allowing statistics to be reported
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using the <<chronyc.adoc#clients,*clients*>> command in *chronyc*.
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using the <<chronyc.adoc#clients,*clients*>> command in *chronyc*.
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[[local]]*local* *stratum* _stratum_::
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[[local]]*local* [_option_]...::
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The *local* directive is used to allow *chronyd* to appear synchronised to real
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The *local* directive enables a local reference mode, which allows *chronyd*
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time (from the viewpoint of clients polling it), even if it has no current
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operating as an NTP server to appear synchronised to real time (from the
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synchronisation source.
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viewpoint of clients polling it), even when it was never synchronised or
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the last update of the clock happened long time ago.
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This directive is normally used on computers in an isolated network, where
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This directive is normally used in an isolated network, where computers are
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several computers are required to synchronise to one other, this being the
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required to be synchronised to one another, but not necessarily to real time.
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'`master`' which is kept vaguely in line with real time by manual input.
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The server may be kept vaguely in line with real time by manual input.
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The *local* directive has the following options:
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*stratum* _stratum_:::
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This option sets the stratum of the server which will be reported to clients
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when the local reference is active. The specified value is in the range 1
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through 15, and the default value is 10. It should be larger than the maximum
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expected stratum in the network when external NTP servers are accessible.
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Stratum 1 indicates a computer that has a true real-time reference directly
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connected to it (e.g. GPS, atomic clock, etc), such computers are expected to
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be very close to real time. Stratum 2 computers are those which have a stratum
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1 server; stratum 3 computers have a stratum 2 server and so on. A large value
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of 10 indicates that the clock is so many hops away from a reference clock that
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its time is fairly unreliable.
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*distance* _distance_:::
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This option sets the threshold for root distance which will activate the local
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reference. If *chronyd* was synchronised to some source, the local reference
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will not be actived until its root distance reaches the specified value (the
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rate at which the distance is increasing depends on how well the clock was
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tracking the source). The default value is 1 second.
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The current root distance can be calculated from root delay and root dispersion
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(reported by the <<chronyc.adoc#tracking,*tracking*>> command in *chronyc*) as
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----
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distance = delay / 2 + dispersion
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----
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*orphan*:::
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This option enables a special '`orphan`' mode, where sources with stratum equal
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to the local _stratum_ are assumed to not serve real time. They are ignored
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unless no other source is selectable and their reference IDs are smaller than
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the local reference ID.
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This allows multiple servers in the network to use the same *local*
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configuration and be synchronised to one another, without confusing clients
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that poll more than one server. Each server needs to be configured to poll all
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other servers with the *local* directive. This ensures only the server with the
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smallest reference ID has the local reference active and others are
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synchronised to it. When that server fails, another will take over.
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The *orphan* mode is compatible with the *ntpd*'s orphan mode (enabled by the
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*tos orphan* command).
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An example of the directive is
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An example of the directive is
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----
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----
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local stratum 10
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local stratum 10 orphan
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----
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----
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The value 10 may be substituted with other values in the range 1 through 15.
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Stratum 1 indicates a computer that has a true real-time reference directly
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connected to it (e.g. GPS, atomic clock etc), such computers are expected to be
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very close to real time. Stratum 2 computers are those which have a stratum 1
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server; stratum 3 computers have a stratum 2 server and so on.
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A large value of 10 indicates that the clock is so many hops away from a
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reference clock that its time is fairly unreliable. Put another way, if the
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computer ever has access to another computer which is ultimately synchronised
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to a reference clock, it will almost certainly be at a stratum less than 10.
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Therefore, the choice of a high value like 10 for the *local* directive
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prevents the machine's own time from ever being confused with real time, were
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it ever to leak out to clients that have visibility of real servers.
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[[port]]*port* _port_::
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[[port]]*port* _port_::
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This option allows you to configure the port on which *chronyd* will listen for
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This option allows you to configure the port on which *chronyd* will listen for
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