segments
        are sent to archive storage by setting
        <xref linkend="guc-archive-command"/> or
        <xref linkend="guc-archive-library"/>. In addition to <literal>off</literal>,
        to disable, there are two modes: <literal>on</literal>, and
        <literal>always</literal>. During normal operation, there is no
        difference between the two modes, but when set to <literal>always</literal>
        the WAL archiver is enabled also during archive recovery or standby
        mode. In <literal>always</literal> mode, all files restored from the archive
        or streamed with streaming replication will be archived (again). See
        <xref linkend="continuous-archiving-in-standby"/> for details.
       </para>
       <para>
        <varname>archive_mode</varname> is a separate setting from
        <varname>archive_command</varname> and
        <varname>archive_library</varname> so that
        <varname>archive_command</varname> and
        <varname>archive_library</varname> can be changed without leaving
        archiving mode.
        This parameter can only be set at server start.
        <varname>archive_mode</varname> cannot be enabled when
        <varname>wal_level</varname> is set to <literal>minimal</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-archive-command" xreflabel="archive_command">
      <term><varname>archive_command</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>archive_command</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The local shell command to execute to archive a completed WAL file
        segment.  Any <literal>%p</literal> in the string is
        replaced by the path name of the file to archive, and any
        <literal>%f</literal> is replaced by only the file name.
        (The path name is relative to the working directory of the server,
        i.e., the cluster's data directory.)
        Use <literal>%%</literal> to embed an actual <literal>%</literal> character in the
        command.  It is important for the command to return a zero
        exit status only if it succeeds. For more information see
        <xref linkend="backup-archiving-wal"/>.
       </para>
       <para>
        This parameter can only be set in the <filename>postgresql.conf</filename>
        file or on the server command line.  It is only used if
        <varname>archive_mode</varname> was enabled at server start and
        <varname>archive_library</varname> is set to an empty string.  If both
        <varname>archive_command</varname> and <varname>archive_library</varname>
        are set, an error will be raised.
        If <varname>archive_command</varname> is an empty string (the default) while
        <varname>archive_mode</varname> is enabled (and <varname>archive_library</varname>
        is set to an empty string), WAL archiving is temporarily
        disabled, but the server continues to accumulate WAL segment files in
        the expectation that a command will soon be provided.  Setting
        <varname>archive_command</varname> to a command that does nothing but
        return true, e.g., <literal>/bin/true</literal> (<literal>REM</literal> on
        Windows), effectively disables
        archiving, but also breaks the chain of WAL files needed for
        archive recovery, so it should only be used in unusual circumstances.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry id="guc-archive-library" xreflabel="archive_library">
      <term><varname>archive_library</varname> (<type>string</type>)
      <indexterm>
       <primary><varname>archive_library</varname> configuration parameter</primary>
      </indexterm>
      </term>
      <listitem>
       <para>
        The library to use for archiving completed WAL file segments.  If set to
        an empty string (the default), archiving via shell is enabled, and
        <xref