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doc: improve chrony.conf man page

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Miroslav Lichvar 2017-01-06 11:06:42 +01:00
parent cacbe9976f
commit 042c670747
1 changed files with 28 additions and 14 deletions
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doc/chrony.conf.adoc
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@ -160,9 +160,8 @@ synchronisation only if they agree with the trusted and required source.
*xleave*:::
This option enables an interleaved mode which allows the server or the peer to
send transmit timestamps captured after the actual transmission (e.g. when the
server or the peer is running *chronyd* with HW timestamping enabled by the
<<hwtimestamp,*hwtimestamp*>> directive). This can significantly improve the
accuracy of the measurements.
server or the peer is running *chronyd* with software (kernel) or hardware
timestamping). This can significantly improve the accuracy of the measurements.
+
The interleaved mode is compatible with servers that support only the basic
mode, but peers must both support and have enabled the interleaved mode,
@ -994,7 +993,7 @@ both a client of its servers, and a server to other clients.
Examples of the use of the directive are as follows:
+
----
allow foo.example.net
allow 1.2.3.4
allow 1.2
allow 3.4.5
allow 6.7.8/22
@ -1005,7 +1004,8 @@ allow ::/0
allow
----
+
The first directive allows the named node to be an NTP client of this computer.
The first directive allows a node with IPv4 address _1.2.3.4_ to be an NTP
client of this computer.
The second directive allows any node with an IPv4 address of the form _1.2.x.y_
(with _x_ and _y_ arbitrary) to be an NTP client of this computer. Likewise,
the third directive allows any node with an IPv4 address of the form _3.4.5.x_
@ -1046,6 +1046,10 @@ Within a configuration file this capability is probably rather moot; however,
it is of greater use for reconfiguration at run-time via *chronyc* with the
<<chronyc.adoc#allow,*allow all*>> command.
+
The directive allows a hostname to be specified instead of an IP address, but
the name must be resolvable when *chronyd* is started (i.e. *chronyd* needs
to be started when the network is already up and DNS is working).
+
Note, if the <<initstepslew,*initstepslew*>> directive is used in the
configuration file, each of the computers listed in that directive must allow
client access by this computer for it to work.
@ -2234,24 +2238,34 @@ information to be saved.
*chronyd* can be configured to operate as a public NTP server, e.g. to join the
http://www.pool.ntp.org/en/join.html[pool.ntp.org] project. The configuration
is similar to the NTP client with permanent connection, except it needs to
allow client access from all addresses. It is recommended to handpick at least
few good servers, and possibly combine them with a random selection of other
servers in the pool. Rate limiting can be enabled to not waste too much
bandwidth on misconfigured and broken NTP clients. The *-r* option with the
*dumpdir* directive shortens the time for which *chronyd* will not serve time
to its clients when it needs to be restarted for any reason.
allow client access from all addresses. It is recommended to find at least four
good servers (e.g. from the pool, or on the NTP homepage). If the server has a
hardware reference clock (e.g. a GPS receiver), it can be specified by the
<<refclock,*refclock*>> directive.
The configuration file might be:
The amount of memory used for logging client accesses can be increased in order
to enable clients to use the interleaved mode even when the server has a large
number of clients, and better support rate limiting if it is enabled by the
<<ratelimit,*ratelimit*>> directive. The system timezone database, if it is
kept up to date and includes the *right/UTC* timezone, can be used as a
reliable source to determine when a leap second will be applied to UTC. The
*-r* option with the <<dumpdir,*dumpdir*>> directive shortens the time in which
*chronyd* will not be able to serve time to its clients when it needs to be
restarted (e.g. after upgrading to a newer version, or a change in the
configuration).
The configuration file could look like:
----
server foo.example.net iburst
server bar.example.net iburst
server baz.example.net iburst
pool pool.ntp.org iburst
server qux.example.net iburst
makestep 1.0 3
rtcsync
allow
ratelimit interval 2 burst 10
clientloglimit 100000000
leapsectz right/UTC
driftfile @CHRONYVARDIR@/drift
dumpdir @CHRONYRUNDIR@
dumponexit