<!--
doc/src/sgml/ref/pg_basebackup.sgml
PostgreSQL documentation
-->

<refentry id="app-pgbasebackup">
 <indexterm zone="app-pgbasebackup">
  <primary>pg_basebackup</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>pg_basebackup</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 base backups of
   a running <productname>PostgreSQL</productname> database cluster. These
   are taken without affecting other clients to 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
   servers (see <xref linkend="warm-standby"/>).
  </para>

  <para>
   <application>pg_basebackup</application> makes a binary copy of the database
   cluster files, while making sure the system is put in 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 individual database backups, a tool such as
   <xref linkend="app-pgdump"/> must be used.
  </para>

  <para>
   The backup is made over a regular <productname>PostgreSQL</productname>
   connection, and uses the replication protocol. The connection must be made
   with a superuser or a user having <literal>REPLICATION</literal>
   permissions (see <xref linkend="role-attributes"/>),
   and <filename>pg_hba.conf</filename> must explicitly permit the replication
   connection. The server must also be configured
   with <xref linkend="guc-max-wal-senders"/> set high enough to leave at least
   one session available for the backup and 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
   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 master 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 <link linkend="auth-pg-hba-conf">host-based authentication</link>).
   You will also need to enable <xref linkend="guc-full-page-writes"/> on the master.
  </para>

  <para>
   Note that there are some limitations in an online backup from the standby:

   <itemizedlist>
    <listitem>
     <para>
      The backup history file is not created in the database cluster backed up.
     </para>
    </listitem>
    <listitem>
     <para>
      If you are using <literal>-X none</literal>, there is no guarantee that all
      WAL files required for the backup are archived at the end of backup.
     </para>
    </listitem>
    <listitem>
     <para>
      If the standby is promoted to the master 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 master 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>
 </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>
        Directory to write the output to.
        <application>pg_basebackup</application> will create the directory and
        any parent directories if necessary.  The directory may already exist,
        but it is an error if the directory already exists and is not empty.
       </para>
       <para>
        When the backup is in tar mode, and the directory is specified as
        <literal>-</literal> (dash), the tar file will 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
            current 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 server.
           </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 will be written to a file named
            <filename>base.tar</filename>, and all other tablespaces will
            be named after the tablespace OID.
            </para>
           <para>
            If the value <literal>-</literal> (dash) is specified as
            target directory, the tar contents will be written to
            standard output, suitable for piping to for example
            <productname>gzip</productname>. This is only possible if
            the cluster has no additional tablespaces and WAL
            streaming is not used.
           </para>
           </listitem>
         </varlistentry>
        </variablelist></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>
        The maximum transfer rate of data transferred from 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>
        The purpose is to limit the impact of <application>pg_basebackup</application>
        on the running server.
       </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>-R</option></term>
      <term><option>--write-recovery-conf</option></term>
      <listitem>

       <para>
        Create <filename>standby.signal</filename> and append connection settings
        to <filename>postgresql.auto.conf</filename> in the output
        directory (or into the base archive file when using tar format) to
        ease setting up a standby server.
        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 the
        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>
        Relocate 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 currently defined.  (But
        it is not an error if there is no tablespace
        in <replaceable>olddir</replaceable> contained in the backup.)
        Both <replaceable>olddir</replaceable>
        and <replaceable>newdir</replaceable> must be absolute paths.  If a
        path happens to contain a <literal>=</literal> sign, escape it with a
        backslash.  This option can be specified multiple times for multiple
        tablespaces.  See examples below.
       </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>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--waldir=<replaceable class="parameter">waldir</replaceable></option></term>
      <listitem>
       <para>
        Specifies the location for the write-ahead log directory.
        <replaceable>waldir</replaceable> must be an absolute path.
        The write-ahead log directory can only be specified when
        the backup is in plain mode.
       </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 write-ahead log files (WAL 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 directly in the extracted
        directory without the need to consult the log archive, thus
        making this a completely standalone backup.
       </para>
       <para>
        The following methods 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 log 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
            <xref linkend="guc-wal-keep-segments"/> parameter to be set high
             enough that the log is not removed before the end of the backup.
             If the log has been rotated when it's time to transfer it, the
             backup will fail and be unusable.
           </para>
           <para>
            When tar format mode is used, the write-ahead log files will be
            written to the <filename>base.tar</filename> file.
           </para>
          </listitem>
         </varlistentry>

         <varlistentry>
          <term><literal>s</literal></term>
          <term><literal>stream</literal></term>
          <listitem>
           <para>
            Stream the write-ahead log while the backup is created. This will
            open a second connection to the server and start streaming the
            write-ahead log in parallel while running the backup. Therefore,
            it will use up two connections configured by the
            <xref linkend="guc-max-wal-senders"/> parameter. As long as the
             client can keep up with write-ahead log received, using this mode
             requires no extra write-ahead logs to be saved on the master.
           </para>
           <para>
            When tar format mode 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 running 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 (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>
        This option causes creation of a replication slot named by the
        <literal>--slot</literal> option 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, data 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>
       <para>
        When this is enabled, 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.
       </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 the WAL streaming to use the specified
        replication slot.  If the base backup is intended to be used as a
        streaming replication standby using replication slots, it should then
        use the same replication slot name
        in <xref linkend="guc-primary-slot-name"/>.  That way, it is ensured that
        the server does not remove any necessary WAL data in the time between
        the end of the base backup and the start of streaming replication.
       </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>--no-slot</option></term>
      <listitem>
       <para>
        This option prevents the creation of a temporary replication slot
        during the backup even if it's supported by the server.
       </para>
       <para>
        Temporary replication slots are created by default if no slot name
        is given with the option <option>-S</option> when using log streaming.
       </para>
       <para>
        The main purpose of this option is to allow taking a base backup when
        the server is out of free replication slots.  Using replication slots
        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.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    The following command-line options control the database connection parameters.

    <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 connection
        string. See <xref linkend="libpq-connstring"/> for more information.
       </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, 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 the 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
        server. This allows for easier monitoring of the progress from server.
        A value of zero disables the periodic status updates completely,
        although an update will still be sent when requested by the server, to
        avoid timeout disconnect. 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>
        User name to connect as.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-w</option></term>
      <term><option>--no-password</option></term>
      <listitem>
       <para>
        Never issue 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>
        Force <application>pg_basebackup</application> to prompt for a
        password before connecting to a database.
       </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>
       Print the <application>pg_basebackup</application> version and exit.
       </para>
       </listitem>
     </varlistentry>

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

 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   At the beginning of the backup, a checkpoint needs to be written on the
   server the backup is taken from.  Especially if the option
   <literal>--checkpoint=fast</literal> is not used, this can take some time
   during which <application>pg_basebackup</application> will be 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>
   Tablespaces will in plain format by default be backed up to the same path
   they have on the 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 mode is used, it is the user's responsibility to unpack each
   tar file before starting the PostgreSQL server. 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 mode
   (<literal>--format=tar</literal>) of the current version only works with server version 9.5
   or later.
  </para>

  <para>
   <application>pg_basebackup</application> will preserve group permissions in
   both the <literal>plain</literal> and <literal>tar</literal> formats 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>
  </simplelist>
 </refsect1>

</refentry>
