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<title>ntpdc - special NTP query program</title>
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<h3><tt>ntpdc</tt> - special NTP query program</h3>
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<img align="left" src="pic/alice31.gif" alt="gif"><a href=
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"http://www.eecis.udel.edu/~mills/pictures.htm">from <i>Alice's
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Adventures in Wonderland</i>, Lewis Carroll</a>
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<p>This program is a big puppy.<br clear="left">
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<tt>ntpdc [ -ilnps ] [ -c <i>command</i> ] [ <i>host</i> ] [ ...
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<tt>ntpdc</tt> is used to query the <tt>ntpd</tt> daemon about its
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current state and to request changes in that state. The program may
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be run either in interactive mode or controlled using command line
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arguments. Extensive state and statistics information is available
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through the <tt>ntpdc</tt> interface. In addition, nearly all the
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configuration options which can be specified at startup using
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ntpd's configuration file may also be specified at run time using
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<p>If one or more request options are included on the command line
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when <tt>ntpdc</tt> is executed, each of the requests will be sent
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to the NTP servers running on each of the hosts given as command
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line arguments, or on localhost by default. If no request options
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are given, <tt>ntpdc</tt> will attempt to read commands from the
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standard input and execute these on the NTP server running on the
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first host given on the command line, again defaulting to localhost
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when no other host is specified. <tt>ntpdc</tt> will prompt for
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commands if the standard input is a terminal device.</p>
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<p><tt>ntpdc</tt> uses NTP mode 7 packets to communicate with the
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NTP server, and hence can be used to query any compatable server on
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the network which permits it. Note that since NTP is a UDP protocol
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this communication will be somewhat unreliable, especially over
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large distances in terms of network topology. <tt>ntpdc</tt> makes
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no attempt to retransmit requests, and will time requests out if
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the remote host is not heard from within a suitable timeout
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<p>The operation of <tt>ntpdc</tt> are specific to the particular
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implementation of the <tt>ntpd</tt> daemon and can be expected to
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work only with this and maybe some previous versions of the daemon.
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Requests from a remote <tt>ntpdc</tt> program which affect the
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state of the local server must be authenticated, which requires
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both the remote program and local server share a common key and key
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<h4>Command Line Options</h4>
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Specifying a command line option other than <tt>-i</tt> or <tt>
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-n</tt> will cause the specified query (queries) to be sent to the
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indicated host(s) immediately. Otherwise, <tt>ntpdc</tt> will
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attempt to read interactive format commands from the standard
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<dt><tt>-c <i>command</i></tt></dt>
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<dd>The following argument is interpreted as an interactive format
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command and is added to the list of commands to be executed on the
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specified host(s). Multiple -c options may be given.</dd>
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<dd>Force <tt>ntpdc</tt> to operate in interactive mode. Prompts
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will be written to the standard output and commands read from the
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<dd>Obtain a list of peers which are known to the server(s). This
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switch is equivalent to <tt>-c listpeers</tt>.</dd>
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<dd>Output all host addresses in dotted-quad numeric format rather
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than converting to the canonical host names.</dd>
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<dd>Print a list of the peers known to the server as well as a
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summary of their state. This is equivalent to <tt>-c
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<dd>Print a list of the peers known to the server as well as a
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summary of their state, but in a slightly different format than the
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-p switch. This is equivalent to <tt>-c dmpeers</tt>.</dd>
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<h4>Interactive Commands</h4>
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Interactive format commands consist of a keyword followed by zero
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to four arguments. Only enough characters of the full keyword to
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uniquely identify the command need be typed. The output of a
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command is normally sent to the standard output, but optionally the
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output of individual commands may be sent to a file by appending a
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<tt><</tt>, followed by a file name, to the command line.
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<p>A number of interactive format commands are executed entirely
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within the <tt>ntpdc</tt> program itself and do not result in NTP
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mode 7 requests being sent to a server. These are described
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<dt><tt>? [ <i>command_keyword</i> ]</tt><br>
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<tt>help [ <i>command_keyword</i> ]</tt></dt>
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<dd>A <tt>?</tt> by itself will print a list of all the command
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keywords known to this incarnation of <tt>ntpq</tt>. A <tt>?</tt>
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followed by a command keyword will print funcation and usage
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information about the command. This command is probably a better
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source of information about <tt>ntpq</tt> than this manual
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<dt><tt>delay <i>milliseconds</i></tt></dt>
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<dd>Specify a time interval to be added to timestamps included in
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requests which require authentication. This is used to enable
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(unreliable) server reconfiguration over long delay network paths
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or between machines whose clocks are unsynchronized. Actually the
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server does not now require timestamps in authenticated requests,
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so this command may be obsolete.</dd>
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<dt><tt>host <i>hostname</i></tt></dt>
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<dd>Set the host to which future queries will be sent. Hostname may
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be either a host name or a numeric address.</dd>
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<dt><tt>hostnames [ yes | no ]</tt></dt>
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<dd>If <tt>yes</tt> is specified, host names are printed in
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information displays. If <tt>no</tt> is specified, numeric
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addresses are printed instead. The default is <tt>yes</tt>, unless
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modified using the command line <tt>-n</tt> switch.</dd>
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<dt><tt>keyid <i>keyid</i></tt></dt>
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<dd>This command allows the specification of a key number to be
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used to authenticate configuration requests. This must correspond
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to a key number the server has been configured to use for this
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<dt><tt>quit</tt></dt>
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<dd>Exit <tt>ntpdc</tt>.</dd>
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<dt><tt>passwd</tt></dt>
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<dd>This command prompts you to type in a password (which will not
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be echoed) which will be used to authenticate configuration
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requests. The password must correspond to the key configured for
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use by the NTP server for this purpose if such requests are to be
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<dt><tt>timeout <i>millseconds</i></tt></dt>
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<dd>Specify a timeout period for responses to server queries. The
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default is about 8000 milliseconds. Note that since <tt>ntpdc</tt>
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retries each query once after a timeout, the total waiting time for
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a timeout will be twice the timeout value set.</dd>
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<h4>Control Message Commands</h4>
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Query commands result in NTP mode 7 packets containing requests for
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information being sent to the server. These are read-only commands
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in that they make no modification of the server configuration
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<dt><tt>listpeers</tt></dt>
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<dd>Obtains and prints a brief list of the peers for which the
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server is maintaining state. These should include all configured
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peer associations as well as those peers whose stratum is such that
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they are considered by the server to be possible future
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synchonization candidates.</dd>
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<dt><tt>peers</tt></dt>
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<dd>Obtains a list of peers for which the server is maintaining
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state, along with a summary of that state. Summary information
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includes the address of the remote peer, the local interface
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address (0.0.0.0 if a local address has yet to be determined), the
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stratum of the remote peer (a stratum of 16 indicates the remote
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peer is unsynchronized), the polling interval, in seconds, the
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reachability register, in octal, and the current estimated delay,
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offset and dispersion of the peer, all in seconds.
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<p>The character in the left margin indicates the mode this peer
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entry is operating in. A <tt>+</tt> denotes symmetric active, a
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<tt>-</tt> indicates symmetric passive, a <tt>=</tt> means the
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remote server is being polled in client mode, a <tt>^</tt>
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indicates that the server is broadcasting to this address, a <tt>
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~</tt> denotes that the remote peer is sending broadcasts and a
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<tt>*</tt> marks the peer the server is currently synchonizing
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<p>The contents of the host field may be one of four forms. It may
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be a host name, an IP address, a reference clock implementation
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name with its parameter or <tt>REFCLK(<i>implementation number</i>,
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<i>parameter</i>)</tt>. On <tt>hostnames no</tt> only IP-addresses
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will be displayed.</p>
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<dt><tt>dmpeers</tt></dt>
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<dd>A slightly different peer summary list. Identical to the output
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of the <tt>peers</tt> command, except for the character in the
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leftmost column. Characters only appear beside peers which were
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included in the final stage of the clock selection algorithm. A
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<tt>.</tt> indicates that this peer was cast off in the falseticker
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detection, while a <tt>+</tt> indicates that the peer made it
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through. A <tt>*</tt> denotes the peer the server is currently
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synchronizing with.</dd>
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<dt><tt>showpeer <i>peer_address</i> [...]</tt></dt>
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<dd>Shows a detailed display of the current peer variables for one
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or more peers. Most of these values are described in the NTP
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Version 2 specification.</dd>
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<dt><tt>pstats <i>peer_address</i> [...]</tt></dt>
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<dd>Show per-peer statistic counters associated with the specified
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<dt><tt>clockinfo <i>clock_peer_address</i> [...]</tt></dt>
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<dd>Obtain and print information concerning a peer clock. The
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values obtained provide information on the setting of fudge factors
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and other clock performance information.</dd>
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<dt><tt>kerninfo</tt></dt>
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<dd>Obtain and print kernel phase-lock loop operating parameters.
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This information is available only if the kernel has been specially
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modified for a precision timekeeping function.</dd>
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<dt><tt>loopinfo [ oneline | multiline ]</tt></dt>
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<dd>Print the values of selected loop filter variables. The loop
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filter is the part of NTP which deals with adjusting the local
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system clock. The <tt>offset</tt> is the last offset given to the
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loop filter by the packet processing code. The <tt>frequency</tt>
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is the frequency error of the local clock in parts-per-million
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(ppm). The <tt>time_const</tt> controls the stiffness of the
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phase-lock loop and thus the speed at which it can adapt to
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oscillator drift. The <tt>watchdog timer</tt> value is the number
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of seconds which have elapsed since the last sample offset was
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given to the loop filter. The <tt>oneline</tt> and <tt>
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multiline</tt> options specify the format in which this information
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is to be printed, with <tt>multiline</tt> as the default.</dd>
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<dt><tt>sysinfo</tt></dt>
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<dd>Print a variety of system state variables, i.e., state related
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to the local server. All except the last four lines are described
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in the NTP Version 3 specification, RFC-1305.
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<p>The <tt>system flags</tt> show various system flags, some of
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which can be set and cleared by the <tt>enable</tt> and <tt>
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disable</tt> configuration commands, respectively. These are the
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<tt>auth</tt>, <tt>bclient</tt>, <tt>monitor</tt>, <tt>pll</tt>,
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<tt>pps</tt> and <tt>stats</tt> flags. See the <tt>ntpd</tt>
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documentation for the meaning of these flags. There are two
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additional flags which are read only, the <tt>kernel_pll</tt> and
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<tt>kernel_pps</tt>. These flags indicate the synchronization
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status when the precision time kernel modifications are in use. The
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<tt>kernel_pll</tt> indicates that the local clock is being
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disciplined by the kernel, while the kernel_pps indicates the
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kernel discipline is provided by the PPS signal.</p>
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<p>The <tt>stability</tt> is the residual frequency error remaining
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afterthe system frequency correction is applied and is intended for
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maintenance and debugging. In most architectures, this value will
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initially decrease from as high as 500 ppm to a nominal value in
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the range .01 to 0.1 ppm. If it remains high for some time after
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starting the daemon, something may be wrong with the local clock,
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or the value of the kernel variable <tt>tick</tt> may be
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<p>The <tt>broadcastdelay</tt> shows the default broadcast delay,
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as set by the <tt>broadcastdelay</tt> configuration command.</p>
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<p>The <tt>authdelay</tt> shows the default authentication delay,
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as set by the <tt>authdelay</tt> configuration command.</p>
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<dt><tt>sysstats</tt></dt>
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<dd>Print statistics counters maintained in the protocol
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<dt><tt>memstats</tt></dt>
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<dd>Print statistics counters related to memory allocation
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<dt><tt>iostats</tt></dt>
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<dd>Print statistics counters maintained in the input-output
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<dt><tt>timerstats</tt></dt>
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<dd>Print statistics counters maintained in the timer/event queue
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<dt><tt>reslist</tt></dt>
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<dd>Obtain and print the server's restriction list. This list is
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(usually) printed in sorted order and may help to understand how
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the restrictions are applied.</dd>
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<dt><tt>monlist [ <i>version</i> ]</tt></dt>
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<dd>Obtain and print traffic counts collected and maintained by the
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monitor facility. The version number should not normally need to be
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<dt><tt>clkbug <i>clock_peer_address</i> [...]</tt></dt>
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<dd>Obtain debugging information for a reference clock driver. This
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information is provided only by some clock drivers and is mostly
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undecodable without a copy of the driver source in hand.</dd>
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<h4>Runtime Configuration Requests</h4>
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All requests which cause state changes in the server are
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authenticated by the server using a configured NTP key (the
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facility can also be disabled by the server by not configuring a
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key). The key number and the corresponding key must also be made
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known to xtnpdc. This can be done using the keyid and passwd
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commands, the latter of which will prompt at the terminal for a
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password to use as the encryption key. You will also be prompted
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automatically for both the key number and password the first time a
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command which would result in an authenticated request to the
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server is given. Authentication not only provides verification that
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the requester has permission to make such changes, but also gives
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an extra degree of protection again transmission errors.
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<p>Authenticated requests always include a timestamp in the packet
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data, which is included in the computation of the authentication
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code. This timestamp is compared by the server to its receive time
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stamp. If they differ by more than a small amount the request is
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rejected. This is done for two reasons. First, it makes simple
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replay attacks on the server, by someone who might be able to
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overhear traffic on your LAN, much more difficult. Second, it makes
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it more difficult to request configuration changes to your server
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from topologically remote hosts. While the reconfiguration facility
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will work well with a server on the local host, and may work
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adequately between time-synchronized hosts on the same LAN, it will
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work very poorly for more distant hosts. As such, if reasonable
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passwords are chosen, care is taken in the distribution and
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protection of keys and appropriate source address restrictions are
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applied, the run time reconfiguration facility should provide an
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adequate level of security.</p>
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<p>The following commands all make authenticated requests.</p>
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<dt><tt>addpeer <i>peer_address</i> [ <i>keyid</i> ] [ <i>
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version</i> ] [ <i>prefer</i> ]</tt></dt>
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<dd>Add a configured peer association at the given address and
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operating in symmetric active mode. Note that an existing
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association with the same peer may be deleted when this command is
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executed, or may simply be converted to conform to the new
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configuration, as appropriate. If the optional <tt>keyid</tt> is a
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nonzero integer, all outgoing packets to the remote server will
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have an authentication field attached encrypted with this key. If
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the value is 0 (or not given) no authentication will be done. The
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<tt>version#</tt> can be 1, 2 or 3 and defaults to 3. The <tt>
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prefer</tt> keyword indicates a preferred peer (and thus will be
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used primarily for clock synchronisation if possible). The
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preferred peer also determines the validity of the PPS signal - if
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the preferred peer is suitable for synchronisation so is the PPS
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<dt><tt>addserver <i>peer_address</i> [ <i>keyid</i> ] [ <i>
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version</i> ] [ <i>prefer</i> ]</tt></dt>
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<dd>Identical to the addpeer command, except that the operating
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<dt><tt>broadcast <i>peer_address</i> [ <i>keyid</i> ] [ <i>
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version</i> ] [ <i>prefer</i> ]</tt></dt>
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<dd>Identical to the addpeer command, except that the operating
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mode is broadcast. In this case a valid key identifier and key are
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required. The <tt>peer_address</tt> parameter can be the broadcast
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address of the local network or a multicast group address assigned
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to NTP. If a multicast address, a multicast-capable kernel is
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<dt><tt>unconfig <i>peer_address</i> [...]</tt></dt>
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<dd>This command causes the configured bit to be removed from the
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specified peer(s). In many cases this will cause the peer
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association to be deleted. When appropriate, however, the
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association may persist in an unconfigured mode if the remote peer
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is willing to continue on in this fashion.</dd>
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<dt><tt>fudge <i>peer_address</i> [ <i>time1</i> ] [ <i>time2</i> ]
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[ <i>stratum</i> ] [ <i>refid</i> ]</tt></dt>
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<dd>This command provides a way to set certain data for a reference
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clock. See the source listing for further information.</dd>
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<dt><tt>enable [ <i>flag</i> ] [ ... ]</tt><br>
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<tt>disable [ <i>flag</i> ] [ ... ]</tt></dt>
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<dd>These commands operate in the same way as the <tt>enable</tt>
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and <tt>disable</tt> configuration file commands of <tt>ntpd</tt>.
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Following is a description of the flags. Note that only the <tt>
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auth</tt>, <tt>bclient</tt>, <tt>monitor</tt>, <tt>pll</tt>, <tt>
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pps</tt> and <tt>stats</tt> flags can be set by <tt>ntpdc</tt>; the
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<tt>pll_kernel</tt> and <tt>pps_kernel</tt> flags are
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<dt><tt>auth</tt></dt>
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<dd>Enables the server to synchronize with unconfigured peers only
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if the peer has been correctly authenticated using a trusted key
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and key identifier. The default for this flag is enable.</dd>
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<dt><tt>bclient</tt></dt>
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<dd>Enables the server to listen for a message from a broadcast or
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multicast server, as in the <tt>multicastclient</tt> command with
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default address. The default for this flag is disable.</dd>
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<dt><tt>monitor</tt></dt>
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<dd>Enables the monitoring facility. See the <tt>ntpdc</tt> program
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and the <tt>monlist</tt> command or further information. The
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default for this flag is enable.</dd>
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<dt><tt>pll</tt></dt>
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<dd>Enables the server to adjust its local clock by means of NTP.
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If disabled, the local clock free-runs at its intrinsic time and
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frequency offset. This flag is useful in case the local clock is
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controlled by some other device or protocol and NTP is used only to
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provide synchronization to other clients. In this case, the local
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clock driver is used. See the <a href="refclock.htm">Reference
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Clock Drivers</a> page for further information. The default for
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this flag is enable.</dd>
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<dt><tt>pps</tt></dt>
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<dd>Enables the pulse-per-second (PPS) signal when frequency and
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time is disciplined by the precision time kernel modifications. See
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the <a href="kern.htm">A Kernel Model for Precision Timekeeping</a>
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page for further information. The default for this flag is
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<dt><tt>stats</tt></dt>
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<dd>Enables the statistics facility. See the <a href="monopt.htm">
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Monitoring Options</a> page for further information. The default
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for this flag is enable.</dd>
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<dt><tt>pll_kernel</tt></dt>
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<dd>When the precision time kernel modifications are installed,
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this indicates the kernel controls the clock discipline; otherwise,
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the daemon controls the clock discipline.</dd>
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<dt><tt>pps_kernel</tt></dt>
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<dd>When the precision time kernel modifications are installed and
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a pulse-per-second (PPS) signal is available, this indicates the
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PPS signal controls the clock discipline; otherwise, the daemon or
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kernel controls the clock discipline, as indicated by the <tt>
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pll_kernel</tt> flag.</dd>
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<dt><tt>restrict <i>address mask flag</i> [ <i>flag</i> ]</tt></dt>
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<dd>This command operates in the same way as the <tt>restrict</tt>
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configuration file commands of <tt>ntpd</tt>.</dd>
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<dt><tt>unrestrict <i>address mask flag</i> [ <i>flag</i>
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<dd>Unrestrict the matching entry from the restrict list.</dd>
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<dt><tt>delrestrict <i>address mask [ ntpport ]</i></tt></dt>
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<dd>Delete the matching entry from the restrict list.</dd>
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<dt><tt>readkeys</tt></dt>
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<dd>Causes the current set of authentication keys to be purged and
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a new set to be obtained by rereading the keys file (which must
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have been specified in the <tt>ntpd</tt> configuration file). This
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allows encryption keys to be changed without restarting the
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<dt><tt>trustedkey <i>keyid</i> [...]</tt></dt>
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<dt><tt>untrustedkey <i>keyid</i> [...]</tt></dt>
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<dd>These commands operate in the same way as the <tt>
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trustedkey</tt> and <tt>untrustedkey</tt> configuration file
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commands of <tt>ntpd</tt>.</dd>
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<dt><tt>authinfo</tt></dt>
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<dd>Returns information concerning the authentication module,
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including known keys and counts of encryptions and decryptions
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which have been done.</dd>
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<dt><tt>traps</tt></dt>
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<dd>Display the traps set in the server. See the source listing for
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further information.</dd>
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<dt><tt>addtrap [ <i>address</i> [ <i>port</i> ] [ <i>interface</i>
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<dd>Set a trap for asynchronous messages. See the source listing
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for further information.</dd>
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<dt><tt>clrtrap [ <i>address</i> [ <i>port</i> ] [ <i>
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interface</i>]</tt></dt>
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<dd>Clear a trap for asynchronous messages. See the source listing
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for further information.</dd>
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<dt><tt>reset</tt></dt>
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<dd>Clear the statistics counters in various modules of the server.
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See the source listing for further information.</dd>
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<tt>ntpdc</tt> is a crude hack. Much of the information it shows is
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deadly boring and could only be loved by its implementer. The
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program was designed so that new (and temporary) features were easy
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to hack in, at great expense to the program's ease of use. Despite
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this, the program is occasionally useful.
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<a href="index.htm"><img align="left" src="pic/home.gif" alt=
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<address><a href="mailto:mills@udel.edu">David L. Mills
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<mills@udel.edu></a></address>
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html/ntpdc.htm
