doc/src/sgml/ref/pg_basebackup.sgml

<!--
doc/src/sgml/ref/pg_basebackup.sgml
PostgreSQL documentation
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<refentry id="app-pgbasebackup">
 <indexterm zone="app-pgbasebackup">
  <primary>pg_basebackup</primary>
 </indexterm>

 <refmeta>
  <refentrytitle><application>pg_basebackup</application></refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>pg_basebackup</refname>
  <refpurpose>take a base backup of a <productname>PostgreSQL</productname> cluster</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>pg_basebackup</command>
   <arg rep="repeat"><replaceable>option</replaceable></arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>
  <para>
   <application>pg_basebackup</application> is used to take a base backup of
   a running <productname>PostgreSQL</productname> database cluster. The backup
   is taken without affecting other clients of the database, and can be used
   both for point-in-time recovery (see <xref linkend="continuous-archiving"/>)
   and as the starting point for a log-shipping or streaming-replication standby
   server (see <xref linkend="warm-standby"/>).
  </para>

  <para>
   <application>pg_basebackup</application> makes an exact copy of the database
   cluster's files, while making sure the server is put into and
   out of backup mode automatically. Backups are always taken of the entire
   database cluster; it is not possible to back up individual databases or
   database objects. For selective backups, another tool such as
   <xref linkend="app-pgdump"/> must be used.
  </para>

  <para>
   The backup is made over a regular <productname>PostgreSQL</productname>
   connection that uses the replication protocol. The connection must be made
   with a user ID that has <literal>REPLICATION</literal> permissions
   (see <xref linkend="role-attributes"/>) or is a superuser,
   and <link linkend="auth-pg-hba-conf"><filename>pg_hba.conf</filename></link>
   must permit the replication connection. The server must also be configured
   with <xref linkend="guc-max-wal-senders"/> set high enough to provide at
   least one walsender for the backup plus one for WAL streaming (if used).
  </para>

  <para>
   There can be multiple <command>pg_basebackup</command>s running at the same time, but it is usually
   better from a performance point of view to take only one backup, and copy
   the result.
  </para>

  <para>
   <application>pg_basebackup</application> can make a base backup from
   not only the coordinator but also the standby. To take a backup from the standby,
   set up the standby so that it can accept replication connections (that is, set
   <varname>max_wal_senders</varname> and <xref linkend="guc-hot-standby"/>,
   and configure its <filename>pg_hba.conf</filename> appropriately).
   You will also need to enable <xref linkend="guc-full-page-writes"/> on the coordinator.

  <para>
   Note that there are some limitations in taking a backup from a standby:

   <itemizedlist>
    <listitem>
     <para>
      The backup history file is not created in the database cluster backed up.
     </para>
    </listitem>
    <listitem>
     <para>
      <application>pg_basebackup</application> cannot force the standby
      to switch to a new WAL file at the end of backup.
      When you are using <literal>-X none</literal>, if write activity on
      the primary is low, <application>pg_basebackup</application> may
      need to wait a long time for the last WAL file required for the backup
      to be switched and archived.  In this case, it may be useful to run
      <function>pg_switch_wal</function> on the primary in order to
      trigger an immediate WAL file switch.
     </para>
    </listitem>
    <listitem>
     <para>
      If the standby is promoted to the coordinator during online backup, the backup fails.
     </para>
    </listitem>
    <listitem>
     <para>
      All WAL records required for the backup must contain sufficient full-page writes,
      which requires you to enable <varname>full_page_writes</varname> on the coordinator and
      not to use a tool like <application>pg_compresslog</application> as
      <varname>archive_command</varname> to remove full-page writes from WAL files.
     </para>
    </listitem>
   </itemizedlist>
  </para>

  <para>
   Whenever <application>pg_basebackup</application> is taking a base
   backup, the server's <structname>pg_stat_progress_basebackup</structname>
   view will report the progress of the backup.
   See <xref linkend="basebackup-progress-reporting"/> for details.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    The following command-line options control the location and format of the
    output:

    <variablelist>
     <varlistentry>
      <term><option>-D <replaceable class="parameter">directory</replaceable></option></term>
      <term><option>--pgdata=<replaceable class="parameter">directory</replaceable></option></term>
      <listitem>
       <para>
        Sets the target directory to write the output to.
        <application>pg_basebackup</application> will create this directory
        (and any missing parent directories) if it does not exist.  If it
        already exists, it must be empty.
       </para>
       <para>
        When the backup is in tar format, the target directory may be
        specified as <literal>-</literal> (dash), causing the tar file to be
        written to <literal>stdout</literal>.
       </para>
       <para>
        This option is required.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-F <replaceable class="parameter">format</replaceable></option></term>
      <term><option>--format=<replaceable class="parameter">format</replaceable></option></term>
      <listitem>
       <para>
        Selects the format for the output. <replaceable>format</replaceable>
        can be one of the following:

        <variablelist>
         <varlistentry>
          <term><literal>p</literal></term>
          <term><literal>plain</literal></term>
          <listitem>
           <para>
            Write the output as plain files, with the same layout as the
            source server's data directory and tablespaces. When the cluster has
            no additional tablespaces, the whole database will be placed in
            the target directory. If the cluster contains additional
            tablespaces, the main data directory will be placed in the
            target directory, but all other tablespaces will be placed
            in the same absolute path as they have on the source server.
            (See <option>--tablespace-mapping</option> to change that.)
           </para>
           <para>
            This is the default format.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>t</literal></term>
          <term><literal>tar</literal></term>
          <listitem>
           <para>
            Write the output as tar files in the target directory. The main
            data directory's contents will be written to a file named
            <filename>base.tar</filename>, and each other tablespace will be
            written to a separate tar file named after that tablespace's OID.
           </para>
           <para>
            If the target directory is specified as <literal>-</literal>
            (dash), the tar contents will be written to
            standard output, suitable for piping to (for example)
            <productname>gzip</productname>. This is only allowed if
            the cluster has no additional tablespaces and WAL
            streaming is not used.
           </para>
           </listitem>
         </varlistentry>
        </variablelist></para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-R</option></term>
      <term><option>--write-recovery-conf</option></term>
      <listitem>

       <para>
        Creates a
        <link linkend="file-standby-signal"><filename>standby.signal</filename></link>
        <indexterm><primary><filename>standby.signal</filename></primary><secondary>pg_basebackup --write-recovery-conf</secondary></indexterm>
        file and appends
        connection settings to the <filename>postgresql.auto.conf</filename>
        file in the target directory (or within the base archive file when
        using tar format).  This eases setting up a standby server using the
        results of the backup.
       </para>
       <para>
        The <filename>postgresql.auto.conf</filename> file will record the connection
        settings and, if specified, the replication slot
        that <application>pg_basebackup</application> is using, so that
        streaming replication will use the same settings later on.
       </para>

      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-T <replaceable class="parameter">olddir</replaceable>=<replaceable class="parameter">newdir</replaceable></option></term>
      <term><option>--tablespace-mapping=<replaceable class="parameter">olddir</replaceable>=<replaceable class="parameter">newdir</replaceable></option></term>
      <listitem>
       <para>
        Relocates the tablespace in directory <replaceable>olddir</replaceable>
        to <replaceable>newdir</replaceable> during the backup.  To be
        effective, <replaceable>olddir</replaceable> must exactly match the
        path specification of the tablespace as it is defined on the source
        server.  (But it is not an error if there is no tablespace
        in <replaceable>olddir</replaceable> on the source server.)
        Meanwhile <replaceable>newdir</replaceable> is a directory in the
        receiving host's filesystem.  As with the main target directory,
        <replaceable>newdir</replaceable> need not exist already, but if
        it does exist it must be empty.
        Both <replaceable>olddir</replaceable>
        and <replaceable>newdir</replaceable> must be absolute paths.  If
        either path needs to contain an equal sign (<literal>=</literal>),
        precede that with a backslash.  This option can be specified multiple
        times for multiple tablespaces.
       </para>

       <para>
        If a tablespace is relocated in this way, the symbolic links inside
        the main data directory are updated to point to the new location.  So
        the new data directory is ready to be used for a new server instance
        with all tablespaces in the updated locations.
       </para>

       <para>
        Currently, this option only works with plain output format; it is
        ignored if tar format is selected.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--waldir=<replaceable class="parameter">waldir</replaceable></option></term>
      <listitem>
       <para>
        Sets the directory to write WAL (write-ahead log) files to.
        By default WAL files will be placed in
        the <filename>pg_wal</filename> subdirectory of the target
        directory, but this option can be used to place them elsewhere.
        <replaceable>waldir</replaceable> must be an absolute path.
        As with the main target directory,
        <replaceable>waldir</replaceable> need not exist already, but if
        it does exist it must be empty.
        This option can only be specified when
        the backup is in plain format.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-X <replaceable class="parameter">method</replaceable></option></term>
      <term><option>--wal-method=<replaceable class="parameter">method</replaceable></option></term>
      <listitem>
       <para>
        Includes the required WAL (write-ahead log) files in the
        backup. This will include all write-ahead logs generated during
        the backup. Unless the method <literal>none</literal> is specified,
        it is possible to start a postmaster in the target
        directory without the need to consult the log archive, thus
        making the output a completely standalone backup.
       </para>
       <para>
        The following <replaceable>method</replaceable>s for collecting the
        write-ahead logs are supported:

        <variablelist>
         <varlistentry>
          <term><literal>n</literal></term>
          <term><literal>none</literal></term>
          <listitem>
           <para>
            Don't include write-ahead logs in the backup.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>f</literal></term>
          <term><literal>fetch</literal></term>
          <listitem>
           <para>
            The write-ahead log files are collected at the end of the backup.
            Therefore, it is necessary for the source server's
            <xref linkend="guc-wal-keep-size"/> parameter to be set high
            enough that the required log data is not removed before the end
            of the backup.  If the required log data has been recycled
            before it's time to transfer it, the backup will fail and be
            unusable.
           </para>
           <para>
            When tar format is used, the write-ahead log files will be
            included in the <filename>base.tar</filename> file.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>s</literal></term>
          <term><literal>stream</literal></term>
          <listitem>
           <para>
            Stream write-ahead log data while the backup is being taken.
            This method will open a second connection to the server and
            start streaming the write-ahead log in parallel while running
            the backup.  Therefore, it will require two replication
            connections not just one.  As long as the client can keep up
            with the write-ahead log data, using this method requires no
            extra write-ahead logs to be saved on the source server.
           </para>
           <para>
            When tar format is used, the write-ahead log files will be
            written to a separate file named <filename>pg_wal.tar</filename>
            (if the server is a version earlier than 10, the file will be named
            <filename>pg_xlog.tar</filename>).
           </para>
           <para>
            This value is the default.
           </para>
          </listitem>
         </varlistentry>
        </variablelist></para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-z</option></term>
      <term><option>--gzip</option></term>
      <listitem>
       <para>
        Enables gzip compression of tar file output, with the default
        compression level. Compression is only available when using
        the tar format, and the suffix <filename>.gz</filename> will
        automatically be added to all tar filenames.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-Z <replaceable class="parameter">level</replaceable></option></term>
      <term><option>--compress=<replaceable class="parameter">level</replaceable></option></term>
      <listitem>
       <para>
        Enables gzip compression of tar file output, and specifies the
        compression level (0 through 9, 0 being no compression and 9 being best
        compression). Compression is only available when using the tar
        format, and the suffix <filename>.gz</filename> will
        automatically be added to all tar filenames.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
   <para>
    The following command-line options control the generation of the
    backup and the invocation of the program:

    <variablelist>
     <varlistentry>
      <term><option>-c <replaceable class="parameter">fast|spread</replaceable></option></term>
      <term><option>--checkpoint=<replaceable class="parameter">fast|spread</replaceable></option></term>
      <listitem>
       <para>
        Sets checkpoint mode to fast (immediate) or spread (the default)
        (see <xref linkend="backup-lowlevel-base-backup"/>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-C</option></term>
      <term><option>--create-slot</option></term>
      <listitem>
       <para>
        Specifies that the replication slot named by the
        <literal>--slot</literal> option should be created before starting
        the backup.  An error is raised if the slot already exists.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-l <replaceable class="parameter">label</replaceable></option></term>
      <term><option>--label=<replaceable class="parameter">label</replaceable></option></term>
      <listitem>
       <para>
        Sets the label for the backup. If none is specified, a default value of
        <quote><literal>pg_basebackup base backup</literal></quote> will be used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-n</option></term>
      <term><option>--no-clean</option></term>
      <listitem>
       <para>
        By default, when <command>pg_basebackup</command> aborts with an
        error, it removes any directories it might have created before
        discovering that it cannot finish the job (for example, the target
        directory and write-ahead log directory). This option inhibits
        tidying-up and is thus useful for debugging.
       </para>

       <para>
        Note that tablespace directories are not cleaned up either way.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-N</option></term>
      <term><option>--no-sync</option></term>
      <listitem>
       <para>
        By default, <command>pg_basebackup</command> will wait for all files
        to be written safely to disk.  This option causes
        <command>pg_basebackup</command> to return without waiting, which is
        faster, but means that a subsequent operating system crash can leave
        the base backup corrupt.  Generally, this option is useful for testing
        but should not be used when creating a production installation.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-P</option></term>
      <term><option>--progress</option></term>
      <listitem>
       <para>
        Enables progress reporting. Turning this on will deliver an approximate
        progress report during the backup. Since the database may change during
        the backup, this is only an approximation and may not end at exactly
        <literal>100%</literal>. In particular, when WAL log is included in the
        backup, the total amount of data cannot be estimated in advance, and
        in this case the estimated target size will increase once it passes the
        total estimate without WAL.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-r <replaceable class="parameter">rate</replaceable></option></term>
      <term><option>--max-rate=<replaceable class="parameter">rate</replaceable></option></term>
      <listitem>
       <para>
        Sets the maximum transfer rate at which data is collected from the
        source server.  This can be useful to limit the impact
        of <application>pg_basebackup</application> on the server.  Values
        are in kilobytes per second.  Use a suffix of <literal>M</literal>
        to indicate megabytes per second.  A suffix of <literal>k</literal>
        is also accepted, and has no effect.  Valid values are between 32
        kilobytes per second and 1024 megabytes per second.
       </para>
       <para>
        This option always affects transfer of the data directory. Transfer of
        WAL files is only affected if the collection method
        is <literal>fetch</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-S <replaceable>slotname</replaceable></option></term>
      <term><option>--slot=<replaceable class="parameter">slotname</replaceable></option></term>
      <listitem>
       <para>
        This option can only be used together with <literal>-X
        stream</literal>.  It causes WAL streaming to use the specified
        replication slot.  If the base backup is intended to be used as a
        streaming-replication standby using a replication slot, the standby
        should then use the same replication slot name as
        <xref linkend="guc-primary-slot-name"/>.  This ensures that the
        primary server does not remove any necessary WAL data in the time
        between the end of the base backup and the start of streaming
        replication on the new standby.
       </para>
       <para>
        The specified replication slot has to exist unless the
        option <option>-C</option> is also used.
       </para>
       <para>
        If this option is not specified and the server supports temporary
        replication slots (version 10 and later), then a temporary replication
        slot is automatically used for WAL streaming.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-v</option></term>
      <term><option>--verbose</option></term>
      <listitem>
       <para>
        Enables verbose mode. Will output some extra steps during startup and
        shutdown, as well as show the exact file name that is currently being
        processed if progress reporting is also enabled.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--manifest-checksums=<replaceable class="parameter">algorithm</replaceable></option></term>
      <listitem>
       <para>
        Specifies the checksum algorithm that should be applied to each file
        included in the backup manifest. Currently, the available
        algorithms are <literal>NONE</literal>, <literal>CRC32C</literal>,
        <literal>SHA224</literal>, <literal>SHA256</literal>,
        <literal>SHA384</literal>, and <literal>SHA512</literal>.
        The default is <literal>CRC32C</literal>.
       </para>
       <para>
        If <literal>NONE</literal> is selected, the backup manifest will
        not contain any checksums. Otherwise, it will contain a checksum
        of each file in the backup using the specified algorithm. In addition,
        the manifest will always contain a <literal>SHA256</literal>
        checksum of its own contents. The <literal>SHA</literal> algorithms
        are significantly more CPU-intensive than <literal>CRC32C</literal>,
        so selecting one of them may increase the time required to complete
        the backup.
       </para>
       <para>
        Using a SHA hash function provides a cryptographically secure digest
        of each file for users who wish to verify that the backup has not been
        tampered with, while the CRC32C algorithm provides a checksum that is
        much faster to calculate; it is good at catching errors due to accidental
        changes but is not resistant to malicious modifications.  Note that, to
        be useful against an adversary who has access to the backup, the backup
        manifest would need to be stored securely elsewhere or otherwise
        verified not to have been modified since the backup was taken.
       </para>
       <para>
        <xref linkend="app-pgverifybackup"/> can be used to check the
        integrity of a backup against the backup manifest.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--manifest-force-encode</option></term>
      <listitem>
       <para>
        Forces all filenames in the backup manifest to be hex-encoded.
        If this option is not specified, only non-UTF8 filenames are
        hex-encoded. This option is mostly intended to test that tools which
        read a backup manifest file properly handle this case.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--no-estimate-size</option></term>
      <listitem>
       <para>
        Prevents the server from estimating the total
        amount of backup data that will be streamed, resulting in the
        <structfield>backup_total</structfield> column in the
        <structname>pg_stat_progress_basebackup</structname> view
        always being <literal>NULL</literal>.
       </para>
       <para>
        Without this option, the backup will start by enumerating
        the size of the entire database, and then go back and send
        the actual contents. This may make the backup take slightly
        longer, and in particular it will take longer before the first
        data is sent. This option is useful to avoid such estimation
        time if it's too long.
       </para>
       <para>
        This option is not allowed when using <option>--progress</option>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--no-manifest</option></term>
      <listitem>
       <para>
        Disables generation of a backup manifest. If this option is not
        specified, the server will generate and send a backup manifest
        which can be verified using <xref linkend="app-pgverifybackup"/>.
        The manifest is a list of every file present in the backup with the
        exception of any WAL files that may be included. It also stores the
        size, last modification time, and an optional checksum for each file.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--no-slot</option></term>
      <listitem>
       <para>
        Prevents the creation of a temporary replication slot
        for the backup.
       </para>
       <para>
        By default, if log streaming is selected but no slot name is given
        with the <option>-S</option> option, then a temporary replication
        slot is created (if supported by the source server).
       </para>
       <para>
        The main purpose of this option is to allow taking a base backup when
        the server has no free replication slots.  Using a replication slot
        is almost always preferred, because it prevents needed WAL from being
        removed by the server during the backup.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--no-verify-checksums</option></term>
      <listitem>
       <para>
        Disables verification of checksums, if they are enabled on the server
        the base backup is taken from.
       </para>
       <para>
        By default, checksums are verified and checksum failures will result
        in a non-zero exit status. However, the base backup will not be
        removed in such a case, as if the <option>--no-clean</option> option
        had been used.  Checksum verification failures will also be reported
        in the <link linkend="monitoring-pg-stat-database-view">
        <structname>pg_stat_database</structname></link> view.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    The following command-line options control the connection to the source
    server:

    <variablelist>
     <varlistentry>
      <term><option>-d <replaceable class="parameter">connstr</replaceable></option></term>
      <term><option>--dbname=<replaceable class="parameter">connstr</replaceable></option></term>
      <listitem>
       <para>
        Specifies parameters used to connect to the server, as a <link
        linkend="libpq-connstring">connection string</link>;  these
        will override any conflicting command line options.
       </para>
       <para>
        The option is called <literal>--dbname</literal> for consistency with other
        client applications, but because <application>pg_basebackup</application>
        doesn't connect to any particular database in the cluster, any database
        name in the connection string will be ignored.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-h <replaceable class="parameter">host</replaceable></option></term>
      <term><option>--host=<replaceable class="parameter">host</replaceable></option></term>
      <listitem>
       <para>
        Specifies the host name of the machine on which the server is
        running.  If the value begins with a slash, it is used as the
        directory for a Unix domain socket. The default is taken
        from the <envar>PGHOST</envar> environment variable, if set,
        else a Unix domain socket connection is attempted.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-p <replaceable class="parameter">port</replaceable></option></term>
      <term><option>--port=<replaceable class="parameter">port</replaceable></option></term>
      <listitem>
       <para>
        Specifies the TCP port or local Unix domain socket file
        extension on which the server is listening for connections.
        Defaults to the <envar>PGPORT</envar> environment variable, if
        set, or a compiled-in default.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-s <replaceable class="parameter">interval</replaceable></option></term>
      <term><option>--status-interval=<replaceable class="parameter">interval</replaceable></option></term>
      <listitem>
       <para>
        Specifies the number of seconds between status packets sent back to
        the source server. Smaller values allow more accurate monitoring of
        backup progress from the server.
        A value of zero disables periodic status updates completely,
        although an update will still be sent when requested by the server, to
        avoid timeout-based disconnects. The default value is 10 seconds.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-U <replaceable>username</replaceable></option></term>
      <term><option>--username=<replaceable class="parameter">username</replaceable></option></term>
      <listitem>
       <para>
        Specifies the user name to connect as.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-w</option></term>
      <term><option>--no-password</option></term>
      <listitem>
       <para>
        Prevents issuing a password prompt.  If the server requires
        password authentication and a password is not available by
        other means such as a <filename>.pgpass</filename> file, the
        connection attempt will fail.  This option can be useful in
        batch jobs and scripts where no user is present to enter a
        password.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-W</option></term>
      <term><option>--password</option></term>
      <listitem>
       <para>
        Forces <application>pg_basebackup</application> to prompt for a
        password before connecting to the source server.
       </para>

       <para>
        This option is never essential, since
        <application>pg_basebackup</application> will automatically prompt
        for a password if the server demands password authentication.
        However, <application>pg_basebackup</application> will waste a
        connection attempt finding out that the server wants a password.
        In some cases it is worth typing <option>-W</option> to avoid the extra
        connection attempt.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    Other options are also available:

    <variablelist>
     <varlistentry>
       <term><option>-V</option></term>
       <term><option>--version</option></term>
       <listitem>
       <para>
       Prints the <application>pg_basebackup</application> version and exits.
       </para>
       </listitem>
     </varlistentry>

     <varlistentry>
       <term><option>-?</option></term>
       <term><option>--help</option></term>
       <listitem>
       <para>
       Shows help about <application>pg_basebackup</application> command line
       arguments, and exits.
       </para>
       </listitem>
     </varlistentry>

    </variablelist>
   </para>

 </refsect1>

 <refsect1>
  <title>Environment</title>

  <para>
   This utility, like most other <productname>PostgreSQL</productname> utilities,
   uses the environment variables supported by <application>libpq</application>
   (see <xref linkend="libpq-envars"/>).
  </para>

  <para>
   The environment variable <envar>PG_COLOR</envar> specifies whether to use
   color in diagnostic messages. Possible values are
   <literal>always</literal>, <literal>auto</literal> and
   <literal>never</literal>.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   At the beginning of the backup, a checkpoint needs to be performed on the
   source server.  This can take some time (especially if the option
   <literal>--checkpoint=fast</literal> is not used), during
   which <application>pg_basebackup</application> will appear to be idle.
  </para>

  <para>
   The backup will include all files in the data directory and tablespaces,
   including the configuration files and any additional files placed in the
   directory by third parties, except certain temporary files managed by
   PostgreSQL.  But only regular files and directories are copied, except that
   symbolic links used for tablespaces are preserved.  Symbolic links pointing
   to certain directories known to PostgreSQL are copied as empty directories.
   Other symbolic links and special device files are skipped.
   See <xref linkend="protocol-replication"/> for the precise details.
  </para>

  <para>
   In plain format, tablespaces will be backed up to the same path
   they have on the source server, unless the
   option <literal>--tablespace-mapping</literal> is used.  Without
   this option, running a plain format base backup on the same host as the
   server will not work if tablespaces are in use, because the backup would
   have to be written to the same directory locations as the original
   tablespaces.
  </para>

  <para>
   When tar format is used, it is the user's responsibility to unpack each
   tar file before starting a PostgreSQL server that uses the data. If there
   are additional tablespaces, the
   tar files for them need to be unpacked in the correct locations. In this
   case the symbolic links for those tablespaces will be created by the server
   according to the contents of the <filename>tablespace_map</filename> file that is
   included in the <filename>base.tar</filename> file.
  </para>

  <para>
   <application>pg_basebackup</application> works with servers of the same
   or an older major version, down to 9.1. However, WAL streaming mode (<literal>-X
   stream</literal>) only works with server version 9.3 and later, and tar format
   (<literal>--format=tar</literal>) only works with server version 9.5
   and later.
  </para>

  <para>
   <application>pg_basebackup</application> will preserve group permissions
   for data files if group permissions are enabled on the source cluster.
  </para>

 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To create a base backup of the server at <literal>mydbserver</literal>
   and store it in the local directory
   <filename>/usr/local/pgsql/data</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -h mydbserver -D /usr/local/pgsql/data</userinput>
</screen>
  </para>

  <para>
   To create a backup of the local server with one compressed
   tar file for each tablespace, and store it in the directory
   <filename>backup</filename>, showing a progress report while running:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D backup -Ft -z -P</userinput>
</screen>
  </para>

  <para>
   To create a backup of a single-tablespace local database and compress
   this with <productname>bzip2</productname>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D - -Ft -X fetch | bzip2 &gt; backup.tar.bz2</userinput>
</screen>
   (This command will fail if there are multiple tablespaces in the
   database.)
  </para>

  <para>
   To create a backup of a local database where the tablespace in
   <filename>/opt/ts</filename> is relocated
   to <filename>./backup/ts</filename>:
<screen>
<prompt>$</prompt> <userinput>pg_basebackup -D backup/data -T /opt/ts=$(pwd)/backup/ts</userinput>
</screen></para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="app-pgdump"/></member>
   <member><xref linkend="basebackup-progress-reporting"/></member>
  </simplelist>
 </refsect1>

</refentry>