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25          <th colspan="3" align="center">LPRng Reference Manual: 5
26          Sep 2003 (For LPRng-3.8.22)</th>
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34          13. Spool Queues and Files</td>
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44      <h1 class="SECT1"><a name="QUEUELOCKFILE">13.2. Queue Lock
45      File</a></h1>
46
47      <ul>
48        <li>
49          <p><var class="LITERAL">spool_lock_file</var><span class=
50          "emphasis"><i class="EMPHASIS">spool queue lock file -
51          default %P</i></span></p>
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56
57      <p>When the <b class="APPLICATION">lpd</b> server starts
58      printing, it will fork individual worker processes to service
59      each queue. To prevent multiple processes from working on the
60      same queue, a printer lock file specified by the <var class=
61      "LITERAL">queue_lock_file</var> option (default <var class=
62      "LITERAL">%P</var> - the %P is expanded to the print queue
63      name) is used. In our example, the lock file would be: <tt
64      class="FILENAME">/var/lpd/pr/pr</tt>.</p>
65
66      <p>The process ID of the currently active printer is stored
67      in the lock file. By reading the lock file and testing to see
68      if the process is still active, programs such as <b class=
69      "APPLICATION">lpq</b> can determine queue activity.</p>
70
71      <p>Similarly, the worker process may need to create other
72      processes to assist it. These in turn will create lock or
73      temporary files in the spool directory as well.</p>
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