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<th colspan="3" align="center">LPRng-HOWTO: 1 Apr 2002
(For LPRng-3.8.10)</th>
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<div class="SECT1">
<h1 class="SECT1"><a name="QUEUELOCKFILE">13.2. Queue Lock
File</a></h1>
<ul>
<li>
<p><tt class="LITERAL">spool_lock_file</tt><i class=
"EMPHASIS">spool queue lock file - default %P</i></p>
</li>
</ul>
<br>
<br>
<p>When the <b class="APPLICATION">lpd</b> server starts
printing, it will fork individual worker processes to service
each queue. To prevent multiple processes from working on the
same queue, a printer lock file specified by the <tt class=
"LITERAL">queue_lock_file</tt> option (default <tt class=
"LITERAL">%P</tt> - the %P is expanded to the print queue
name) is used. In our example, the lock file would be: <tt
class="FILENAME">/var/lpd/pr/pr</tt>.</p>
<p>The process ID of the currently active printer is stored
in the lock file. By reading the lock file and testing to see
if the process is still active, programs such as <b class=
"APPLICATION">lpq</b> can determine queue activity.</p>
<p>Similarly, the worker process may need to create other
processes to assist it. These in turn will create lock or
temporary files in the spool directory as well.</p>
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