<term><varname>external_pid_file</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>external_pid_file</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        Specifies the name of an additional process-ID (PID) file that the
        server should create for use by server administration programs.
        This parameter can only be set at server start.
       </para>
      </listitem>
     </varlistentry>
     </variablelist>

     <para>
      In a default installation, none of the above parameters are set
      explicitly.  Instead, the
      data directory is specified by the <option>-D</option> command-line
      option or the <envar>PGDATA</envar> environment variable, and the
      configuration files are all found within the data directory.
     </para>

     <para>
      If you wish to keep the configuration files elsewhere than the
      data directory, the <command>postgres</command> <option>-D</option>
      command-line option or <envar>PGDATA</envar> environment variable
      must point to the directory containing the configuration files,
      and the <varname>data_directory</varname> parameter must be set in
      <filename>postgresql.conf</filename> (or on the command line) to show
      where the data directory is actually located.  Notice that
      <varname>data_directory</varname> overrides <option>-D</option> and
      <envar>PGDATA</envar> for the location
      of the data directory, but not for the location of the configuration
      files.
     </para>

     <para>
      If you wish, you can specify the configuration file names and locations
      individually using the parameters <varname>config_file</varname>,
      <varname>hba_file</varname> and/or <varname>ident_file</varname>.
      <varname>config_file</varname> can only be specified on the
      <command>postgres</command> command line, but the others can be
      set within the main configuration file.  If all three parameters plus
      <varname>data_directory</varname> are explicitly set, then it is not necessary
      to specify <option>-D</option> or <envar>PGDATA</envar>.
     </para>

     <para>
      When setting any of these parameters, a relative path will be interpreted
      with respect to the directory in which <command>postgres</command>
      is started.
     </para>
   </sect1>

   <sect1 id="runtime-config-connection">
    <title>Connections and Authentication</title>

    <sect2 id="runtime-config-connection-settings">
     <title>Connection Settings</title>

     <variablelist>

     <varlistentry id="guc-listen-addresses" xreflabel="listen_addresses">
      <term><varname>listen_addresses</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>listen_addresses</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
         Specifies the TCP/IP address(es) on which the server is
         to listen for connections from client applications.
         The value takes the form of a comma-separated list of host names
         and/or numeric IP addresses.  The special entry <literal>*</literal>
         corresponds to all available IP interfaces.  The entry
         <literal>0.0.0.0</literal> allows listening for all IPv4 addresses and
         <literal>::</literal> allows listening for all IPv6 addresses.
         If the list is empty, the server does not listen on any IP interface
         at all, in which case only Unix-domain sockets can be used to connect
         to it.  If the list is not empty, the server will start if it
         can listen on at least one TCP/IP address.  A warning will be
         emitted for any TCP/IP address which cannot be opened.
         The default value is <systemitem class="systemname">localhost</systemitem>,
         which allows only local TCP/IP <quote>loopback</quote> connections to be
         made.
       </para>
       <para>