user.
   This user does not actually have to exist, so the single-user mode
   can be used to manually recover from certain
   kinds of accidental damage to the system catalogs.
  </para>
 </refsect1>

 <refsect1 id="app-postgres-options">
  <title>Options</title>

   <para>
    <command>postgres</command> accepts the following command-line
    arguments.  For a detailed discussion of the options consult <xref
    linkend="runtime-config"/>.  You can save typing most of these
    options by setting up a configuration file.  Some (safe) options
    can also be set from the connecting client in an
    application-dependent way to apply only for that session.  For
    example, if the environment variable <envar>PGOPTIONS</envar> is
    set, then <application>libpq</application>-based clients will pass that
    string to the server, which will interpret it as
    <command>postgres</command> command-line options.
   </para>

   <refsect2>
    <title>General Purpose</title>

    <variablelist>
     <varlistentry>
      <term><option>-B <replaceable class="parameter">nbuffers</replaceable></option></term>
      <listitem>
       <para>
        Sets the number of shared buffers for use by the server
        processes.  The default value of this parameter is chosen
        automatically by <application>initdb</application>.
        Specifying this option is equivalent to setting the
        <xref linkend="guc-shared-buffers"/> configuration parameter.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></option></term>
      <listitem>
       <para>
        Sets a named run-time parameter. The configuration parameters
        supported by <productname>PostgreSQL</productname> are
        described in <xref linkend="runtime-config"/>. Most of the
        other command line options are in fact short forms of such a
        parameter assignment.  <option>-c</option> can appear multiple times
        to set multiple parameters.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-C <replaceable>name</replaceable></option></term>
      <listitem>
       <para>
        Prints the value of the named run-time parameter, and exits.
        (See the <option>-c</option> option above for details.)  This
        returns values from
        <filename>postgresql.conf</filename>, modified by any parameters
        supplied in this invocation.  It does not reflect parameters
        supplied when the cluster was started.
       </para>

       <para>
        This can be used on a running server for most parameters.  However,
        the server must be shut down for some runtime-computed parameters
        (e.g., <xref linkend="guc-shared-memory-size"/>,
        <xref linkend="guc-shared-memory-size-in-huge-pages"/>, and
        <xref linkend="guc-wal-segment-size"/>).
       </para>

       <para>
        This option is meant for other programs that interact with a server
        instance, such as <xref linkend="app-pg-ctl"/>, to query configuration
        parameter values.  User-facing applications should instead use <link
        linkend="sql-show"><command>SHOW</command></link> or the <structname>pg_settings</structname> view.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-d <replaceable>debug-level</replaceable></option></term>
      <listitem>
       <para>
        Sets the debug level.  The higher this value is set, the more
        debugging output is written to the server log.  Values are
        from 1 to 5.  It is also possible to pass <literal>-d
        0</literal> for a specific session, which will prevent the
        server log level of the parent <command>postgres</command> process from being
        propagated to this session.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-D <replaceable class="parameter">datadir</replaceable></option></term>