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  <chapter id="kea-lfc">
    <title>The LFC process</title>

    <section id="kea-lfc-overview">
      <title>Overview</title>
      <para><command>kea-lfc</command> is a service process that removes
      redundant information from the files used to provide persistent storage
      for the memfile data base backend. This service is written to run as a
      stand alone process.  
      </para>
      <para>While <command>kea-lfc</command> can be started externally, there is
      usually no need to do this.  <command>kea-lfc</command> is run on a periodic
      basis by the Kea DHCP servers.
      </para>
      <para>The process operates on a set of files, using them for input and output
      of the lease entries and to indicate where it is in the process in case of an
      interruption.  Currently the caller must supply names for all of the files, in
      the future this requirement may be relaxed with the process getting the names
      from either the configuration file or from defaults.
      </para>
    </section>

    <section id="kea-lfc-usage">
      <title>Command Line Options</title>
      <para><command>kea-lfc</command> is run as follows:
<screen>
kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file
</screen>
      </para>

      <para>The argument <command>-4</command> or <command>-6</command> selects the protocol
      version of the lease files.
      </para>

      <para>The <command>-c</command> argument specifies the configuration file.  This is
      required, but not currently used by the process.
      </para>

      <para>The <command>-p</command> argument specifies the PID file. When the
      <command>kea-lfc</command> process starts it attempts to determine if another
      instance of the process is already running by examining the pid file.  If one
      is already running the new process is terminated.  If one isn't running it writes
      its pid into the pid file.
      </para>

      <para>The other filenames specify where the <command>kea-lfc</command> process
      should look for input, write its output and use for bookkeeping.

        <itemizedlist>
          <listitem><simpara>
            <command>previous</command> &mdash;
            When <command>kea-lfc</command> starts this
            is the result of any previous run of <command>kea-lfc</command>.
            When <command>kea-lfc</command> finishes it is the result of this run.
            If <command>kea-lfc</command> is interrupted before completing,
            this file may not exist.
          </simpara></listitem>

          <listitem><simpara>
            <command>input</command> &mdash;
            Before the DHCP server invokes <command>kea-lfc</command> it will
            move the current lease file here and then call <command>kea-lfc</command>
            with this file.
          </simpara></listitem>

          <listitem><simpara>
            <command>output</command> &mdash;
            The temporary file <command>kea-lfc</command> should use to write the leases.
            Upon completion of writing this file, it will be moved to the finish file
           (see below).
          </simpara></listitem>

          <listitem><simpara>
            <command>finish</command> &mdash;
            Another temporary file <command>kea-lfc</command> uses for bookkeeping.  When
            <command>kea-lfc</command> completes writing the outputfile it moves it to this
            file name.  After <command>kea-lfc</command> finishes deleting the other files
            (previous and input) it moves this file to previous lease file.  By moving the
            files in this fashion the <command>kea-lfc</command> and the DHCP server
            processes can determine the correct file to use even if one of the
            processes was interrupted before completing its task.
          </simpara></listitem>

        </itemizedlist>
      </para>

      <para>There are several additional arguments mostly for debugging purposes.
      <command>-d</command> Sets the logging level to debug. <command>-v</command> and
      <command>-V</command> print out version stamps with <command>-V</command> providing
      a longer form.  <command>-h</command> prints out the usage string.
      </para>

    </section>
  </chapter>
