331 lines
17 KiB
HTML
331 lines
17 KiB
HTML
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<html><head><title>
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Configuration Options
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</title></head><body><h3>
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Configuration Options
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</h3><hr>
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<h4>Configuration Support</h4>
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<p>Following is a description of the configuration commands in
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NTPv4. These commands have the same basic functions as in NTPv3
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and in some cases new functions and new operands. The various
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modes are determined by the command keyword and the type of the
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required IP address. Addresses are classed by type as (s) a
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remote server or peer (IP class A, B and C), (b) the broadcast
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address of a local interface, (m) a multicast address (IP class
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D), or (r) a reference clock address (127.127.x.x). Note that,
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while autokey and burst modes are supported by these commands,
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their effect in some weird mode combinations can be meaningless
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or even destructive.</p>
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<dl>
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<dt><tt>peer </tt><i><tt>address</tt></i><tt> [autokey | key </tt><i><tt>key</tt></i><tt>]
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[burst] [version </tt><i><tt>version</tt></i><tt>]
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[prefer] [minpoll </tt><i><tt>minpoll</tt></i><tt>]</tt><i><tt>
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</tt></i><tt>[maxpoll </tt><i><tt>maxpoll</tt></i><tt>]</tt></dt>
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<dd> </dd>
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<dt><tt>server </tt><i><tt>address</tt></i><tt> [autokey |
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key </tt><i><tt>key</tt></i><tt>] [burst] [version </tt><i><tt>version</tt></i><tt>]
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[prefer] [minpoll </tt><i><tt>minpoll</tt></i><tt>]</tt><i><tt>
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</tt></i><tt>[maxpoll </tt><i><tt>maxpoll</tt></i><tt>]</tt></dt>
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<dd> </dd>
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<dt><tt>broadcast </tt><i><tt>address</tt></i><tt> [autokey |
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key </tt><i><tt>key</tt></i><tt>] [burst] [version </tt><i><tt>version</tt></i><tt>]
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[minpoll </tt><i><tt>minpoll</tt></i><tt>]</tt><i><tt> </tt></i><tt>[maxpoll
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</tt><i><tt>maxpoll</tt></i><tt>] [ttl </tt><i><tt>ttl</tt></i><tt>]</tt></dt>
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<dd> </dd>
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<dt><tt>manycastclient </tt><i><tt>address</tt></i><tt>
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[autokey | key </tt><i><tt>key</tt></i><tt>] [burst]
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[version </tt><i><tt>version</tt></i><tt>] [minpoll </tt><i><tt>minpoll
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</tt></i><tt>[maxpoll </tt><i><tt>maxpoll</tt></i><tt>]
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[ttl </tt><i><tt>ttl</tt></i><tt>]</tt></dt>
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<dd> </dd>
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<dd>These four commands specify the time server name or
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address to be used and the mode in which to operate. The <i><tt>address</tt></i><tt>
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</tt>can be either a DNS name or a IP address in
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dotted-quad notation. Additional information on
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association behavior can be found in the <a
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href="assoc.htm">Association Management</a> page.</dd>
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<dd> </dd>
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<dd><dl>
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<dt><tt>server</tt></dt>
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<dd>For type s and r addresses, this operates as the
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NTPv3 server command, which mobilizes a
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persistent client mode association. The <tt>server</tt>
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command specifies that the local server is to
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operate in client mode with the specified remote
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server. In this mode, the local server can be
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synchronized to the remote server, but the remote
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server can never be synchronized to the local
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server.</dd>
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<dd> </dd>
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<dt><tt>peer</tt></dt>
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<dd>For type s addresses (only), this operates as the
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current <tt>peer </tt>command, which mobilizes a
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persistent symmetric-active mode association,
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except that additional modes are available. This
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command should NOT be used for type b, m or r
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addresses.</dd>
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<dd> </dd>
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<dd>The <tt>peer</tt> command specifies that the
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local server is to operate in symmetric active
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mode with the remote server. In this mode, the
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local server can be synchronized to the remote
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server and, in addition, the remote server can be
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synchronized by the local server. This is useful
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in a network of servers where, depending on
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various failure scenarios, either the local or
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remote server may be the better source of time.</dd>
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<dd> </dd>
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<dt><tt>broadcast</tt></dt>
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<dd>For type b and m addresses (only), this is
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operates as the current NTPv3 <tt>broadcast </tt>command,
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which mobilizes a persistent broadcast mode
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association, except that additional modes are
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available. Multiple commands can be used to
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specify multiple local broadcast interfaces
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(subnets) and/or multiple multicast groups. Note
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that local broadcast messages go only to the
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interface associated with the subnet specified,
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but multicast messages go to all interfaces. In
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the current implementation, the source address
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used for these messages is the Unix host default
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address.</dd>
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<dd> </dd>
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<dd>In broadcast mode, the local server sends
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periodic broadcast messages to a client
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population at the <i><tt>address </tt></i>specified,
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which is usually the broadcast address on (one
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of) the local network(s) or a multicast address
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assigned to NTP. The IANA has assigned the
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multicast group address 224.0.1.1 exclusively to
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NTP, but other nonconflicting addresses can be
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used to contain the messages within
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administrative boundaries.. Ordinarily, this
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specification applies only to the local server
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operating as a sender; for operation as a
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broadcast client, see the <tt>broadcastclient</tt>
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or <tt>multicastclient</tt> commands below.</dd>
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<dd> </dd>
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<dt><tt>manycastclient</tt> </dt>
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<dd>For type m addresses (only), this mobilizes a
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manycast client-mode association for the
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multicast address specified. In this case a
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specific address must be supplied which matches
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the address used on the <tt>manycastserver </tt>command
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for the designated manycast servers. The NTP
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multicast address 224.0.1.1 assigned by the IANA
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should NOT be used, unless specific means are
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taken to avoid spraying large areas of the
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Internet with these messages and causing a
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possibly massive implosion of replies at the
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sender. </dd>
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<dd> </dd>
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<dd>The <tt>manycast </tt>command specifies that the
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local server is to operate in client mode with
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the remote server that are discovered as the
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result of broadcast/multicast messages. The
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client broadcasts a request message to the group
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address associated with the specified <i><tt>address
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</tt></i>and specifically enabled servers respond
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to these messages. The client selects the servers
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providing the best time and continues as with the
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<tt>server </tt>command. The remaining servers
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are discarded as if never heard.</dd>
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<dd> </dd>
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</dl>
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</dd>
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<dd>Options</dd>
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<dd> </dd>
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<dd><dl>
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<dt><tt>autokey</tt></dt>
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<dd>All packets sent to the address are to include
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authentication fields encrypted using the autokey
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scheme.</dd>
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<dd> </dd>
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<dt><tt>burst</tt></dt>
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<dd>At each poll interval, send a burst of eight
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packets spaced, instead of the usual one.</dd>
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<dd> </dd>
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<dt><tt>key </tt><i><tt>key</tt></i></dt>
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<dd>All packets sent to the address are to include
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authentication fields encrypted using the
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specified <i>key</i> identifier, which is an
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unsigned 32-bit integer less than 65536. The
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default is to include no encryption field.</dd>
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<dd> </dd>
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<dt><tt>version </tt><i><tt>version</tt></i></dt>
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<dd>Specifies the version number to be used for
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outgoing NTP packets. Versions 1-4 are the
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choices, with version 4 the default.</dd>
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<dd> </dd>
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<dt><tt>prefer</tt></dt>
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<dd>Marks the server as preferred. All other things
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being equal, this host will be chosen for
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synchronization among a set of correctly
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operating hosts. See the <a href="prefer.htm">Mitigation
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Rules and the <tt>prefer</tt> Keyword </a>page
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for further information.</dd>
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<dd> </dd>
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<dt><tt>ttl </tt><i><tt>ttl</tt></i></dt>
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<dd>This option is used only with broadcast mode. It
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specifies the time-to-live <i><tt>ttl</tt></i> to
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use on multicast packets. Selection of the proper
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value, which defaults to 127, is something of a
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black art and must be coordinated with the
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network administrator.</dd>
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<dd> </dd>
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<dt><tt>minpoll </tt><i><tt>minpoll</tt></i></dt>
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<dt><tt>maxpoll </tt><i><tt>maxpoll</tt></i></dt>
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<dd>These options specify the minimum and maximum
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polling intervals for NTP messages, in seconds to
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the power of two. The default range is 6 (64 s)
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to 10 (1,024 s).The allowable range is 4 (16 s)
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to 17 (36.4 h) inclusive.</dd>
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<dd> </dd>
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</dl>
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</dd>
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<dt><tt>broadcastclient</tt></dt>
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<dd>This command directs the local server to listen for and
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respond to broadcast messages received on any local
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interface. Upon hearing a broadcast message for the first
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time, the local server measures the nominal network delay
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using a brief client/server exchange with the remote
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server, then enters the broadcastclient mode, in which it
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listens for and synchronizes to succeeding broadcast
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messages. Note that, in order to avoid accidental or
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malicious disruption in this mode, both the local and
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remote servers should operate using authentication and
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the same trusted key and key identifier.</dd>
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<dd> </dd>
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<dt><tt>multicastclient [</tt><i><tt>address</tt></i><tt>]
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[...]</tt></dt>
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<dd>This command directs the local server to listen for
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multicast messages at the group address(es) of the global
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network. The default address is that assigned by the
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Numbers Czar to NTP (224.0.1.1). This command operates in
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the same way as the <tt>broadcastclient</tt> command, but
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uses IP multicasting. Support for this command requires a
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multicast kernel.</dd>
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<dd> </dd>
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<dt><tt>driftfile </tt><i><tt>driftfile</tt></i></dt>
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<dd>This command specifies the name of the file used to
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record the frequency offset of the local clock
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oscillator. If the file exists, it is read at startup in
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order to set the initial frequency offset and then
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updated once per hour with the current frequency offset
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computed by the daemon. If the file does not exist or
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this command is not given, the initial frequency offset
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is assumed zero. In this case, it may take some hours for
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the frequency to stabilize and the residual timing errors
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to subside.</dd>
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<dd> </dd>
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<dd>The file format consists of a single line containing a
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single floating point number, which records the frequency
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offset measured in parts-per-million (PPM). The file is
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updated by first writing the current drift value into a
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temporary file and then renaming this file to replace the
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old version. This implies that <tt>ntpd</tt> must have
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write permission for the directory the drift file is
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located in, and that file system links, symbolic or
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otherwise, should be avoided.</dd>
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<dd> </dd>
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<dt><tt>manycastserver </tt><i><tt>address </tt></i><tt>[...]</tt></dt>
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<dd>This command directs the local server to listen for and
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respond to broadcast messages received on any local
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interface, and in addition enables the server to respond
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to client mode messages to the multicast group
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address(es) (type m) specified. At least one address is
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required, but The NTP multicast address 224.0.1.1
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assigned by the IANA should NOT be used, unless specific
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means are taken to limit the span of the reply and avoid
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a possibly massive implosion at the original sender.</dd>
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<dd> </dd>
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<dt><tt>revoke [</tt><i><tt>logsec</tt></i><tt>]</tt> </dt>
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<dd>Specifies the interval between recomputations of the
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private value used with the autokey feature, which
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ordinarily requires an expensive public- key computation.
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The default value is 12 (65,536 s or about 18 hours). For
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poll intervals above the specified interval, a new
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private value will be recomputed for every message sent.</dd>
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<dd> </dd>
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<dt><tt>autokey [</tt><i><tt>logsec</tt></i><tt>]</tt> </dt>
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<dd>Specifies the interval between regenerations of the
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session key list used with the autokey feature. Note that
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the size of the key list for each association depends on
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this interval and the current poll interval. The default
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value is 12 (4096 s or about 1.1 hours). For poll
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intervals above the specified interval, a session key
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list with a single entry will be regenerated for every
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message sent.</dd>
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<dd> </dd>
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<dt><tt>enable [auth | bclient | kernel | monitor | ntp |
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stats]</tt></dt>
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<dt><tt>disable [auth | bclient | kernel | monitor | ntp |
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stats</tt><font face="Courier New">] </font></dt>
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<dd>Provides a way to enable or disable various server
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options. Flags not mentioned are unaffected. Note that
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all of these flags can be controlled remotely using the <a
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href="ntpdc.htm"><tt>ntpdc</tt></a> utility program.</dd>
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<dd> </dd>
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<dd><dl>
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<dt><tt>auth</tt></dt>
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<dd>Enables the server to synchronize with
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unconfigured peers only if the peer has been
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correctly authenticated using a trusted key and
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key identifier. The default for this flag is
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enable.</dd>
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<dd> </dd>
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<dt><tt>bclient</tt></dt>
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<dd>When enabled, this is identical to the <tt>broadcastclient</tt>
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command. The default for this flag is disable.</dd>
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<dd> </dd>
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<dt><tt>kernel</tt></dt>
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<dd>Enables the precision-time kernel support for the
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<tt>ntp_adjtime()</tt> system call, if
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implemented. Ordinarily, support for this routine
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is detected automatically when the NTP daemon is
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compiled, so it is not necessary for the user to
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worry about this flag. It flag is provided
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primarily so that this support can be disabled
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during kernel development.</dd>
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<dd> </dd>
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<dt><tt>monitor</tt></dt>
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<dd>Enables the monitoring facility. See the <tt>ntpdc</tt>
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program and the <tt>monlist</tt> command or
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further information. The default for this flag is
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enable.</dd>
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<dd> </dd>
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<dt><tt>ntp</tt></dt>
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<dd>Enables the server to adjust its local clock by
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means of NTP. If disabled, the local clock
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free-runs at its intrinsic time and frequency
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offset. This flag is useful in case the local
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clock is controlled by some other device or
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protocol and NTP is used only to provide
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synchronization to other clients. In this case,
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the local clock driver can be used to provide
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this function and also certain time variables for
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error estimates and leap-indicators. See the <a
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href="refclock.htm">Reference Clock Drivers </a>page
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for further information. The default for this
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flag is enable.</dd>
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<dd> </dd>
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<dt><tt>stats</tt></dt>
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<dd>Enables the statistics facility. See the <a
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href="monopt.htm">Monitoring Options </a>page for
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further information. The default for this flag is
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enable.</dd>
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<dd> </dd>
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</dl>
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</dd>
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</dl>
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<hr>
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<address>
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|
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David L. Mills (mills@udel.edu)
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</address>
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</body>
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</html>
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