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<div class="SECT1">
<h1 class="SECT1"><a name="DESTINATIONS">12.13. Dynamic
Routing</a></h1>
<p>Options used:</p>
<ul>
<li>
<p><tt class="LITERAL">destinations=</tt><i class=
"EMPHASIS">destinations for jobs</i></p>
</li>
<li>
<p><tt class="LITERAL">router=</tt><i class=
"EMPHASIS">router program</i></p>
</li>
</ul>
<br>
<br>
<p><b class="APPLICATION">LPRng</b> has the ability to route
a job to one or more destinations in a dynamic manner. This
is not the same as <i class="EMPHASIS">load balancing</i>, as
the destinations are hard coded and not able to be changed.
This is accomplished by having a <tt class=
"LITERAL">router</tt> filter generate a set of destinations.
Here is a sample printcap entry:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN5941"></a>
<pre class="SCREEN">
t2|Test Printer 2
:sd=/var/spool/LPD/t2
:lf=log
:destinations=t1@server1,t1@server2,t1@localhost
:router=/usr/local/LPD/router
</pre>
</div>
<br>
<br>
<p>When a job arrives at the <b class="APPLICATION">lpd</b>
server, the 'router' filter is invoked with the standard
filter options which include the user, host, and other
information obtained from the control file. <span class=
"ACRONYM">STDIN</span> is connected to a temporary copy of
the control file, and the CONTROL environment variable is set
to the value of the actual control file itself.</p>
<p>The routing filter exit status is used as follows:</p>
<ul>
<li>
<p>0 (JSUCC) - normal processing</p>
</li>
<li>
<p>37 (JHOLD) - job is held</p>
</li>
<li>
<p>any other value - job is deleted from queue</p>
</li>
</ul>
<br>
<br>
<p>The router filter writes to <span class=
"ACRONYM">STDOUT</span> a file specifying the destinations
for the job. The destinations entries in this file file have
the following format. Entry order is not important, but each
destination must end with the 'end' tag.</p>
<div class="INFORMALEXAMPLE">
<a name="AEN5956"></a>
<pre class="SCREEN">
dest (destination queue)
copies (number of copies to be made)
priority (priority letter)
X(controlfile modifications)
end
</pre>
</div>
<br>
<br>
<p>Example of router output:</p>
<div class="INFORMALEXAMPLE">
<a name="AEN5959"></a>
<pre class="SCREEN">
dest t1@localhost
copies 2
CA
priority B
end
dest t2@localhost
CZ
priority Z
end
</pre>
</div>
<br>
<br>
<p>In this example, two copies of the job will be sent to the
t1 and t2 spool queue servers. The Class (C letter value) and
job priority information will be rewritten with the indicated
values.</p>
<p>If routing information is specified by the router filter
the job will be sent to the default destination.</p>
<p><b class="APPLICATION">lpq</b> will display job
information in a slightly different format for multiple
destination jobs. For example:</p>
<p class="LITERALLAYOUT">
Printer: t2@h4 'Test Printer 2' (routed/bounce queue to 't1@h2.private')<br>
Queue: 1 printable jobs in queue<br>
Rank Owner/ID Class Job Files Size Time<br>
active papowell@h4+707 A 707 /tmp/hi 3 10:04:49<br>
- actv papowell@h4+707.1 A 707 ->t1@localhost <cpy 1/2> 3 10:04:49<br>
- papowell@lprng2+707.2 A 707 ->t2@localhost 3 10:04:49</p>
<br>
<br>
<p>The routing information is displayed below the main job
information. Each destination will have its transfer status
displayed as it is transferred. By convention, the job
identifier of the routed jobs will have a suffix of the form
.N added; copies will have CN added as well. For example,
papowell@lprng2+707.1C2 will be the job sent to the first
destination, copy two.</p>
<p>Routed jobs can be held, removed, etc., just as normal
jobs. In addition, the individual destination jobs can be
manipulated as well. The LPC functionality has been extended
to recognize destination jobids as well as the main job id
for control and/or selection operations.</p>
<p>The optional <tt class="LITERAL">destinations</tt> entry
specifies the possible set of destinations that the job can
be sent to, and is for informational purposes only. In order
for <b class="APPLICATION">lpq</b> and <b class=
"APPLICATION">lprm</b> to find the job once it has been sent
to <b class="APPLICATION">lpd</b>, <b class=
"APPLICATION">lpq</b> and <b class="APPLICATION">lprm</b>
uses the list of printers in the <tt class=
"LITERAL">destinations</tt>, and iterates over list looking
for the job that you are interested in.</p>
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