<!--
doc/src/sgml/ref/pgupgrade.sgml
PostgreSQL documentation
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<refentry id="pgupgrade">
 <indexterm zone="pgupgrade">
  <primary>pg_upgrade</primary>
 </indexterm>

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

 <refnamediv>
  <refname>pg_upgrade</refname>
  <refpurpose>upgrade a <productname>PostgreSQL</productname> server instance</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>pg_upgrade</command>
   <arg choice="plain"><option>-b</option></arg>
   <arg choice="plain"><replaceable>oldbindir</replaceable></arg>
   <arg choice="plain"><option>-B</option></arg>
   <arg choice="plain"><replaceable>newbindir</replaceable></arg>
   <arg choice="plain"><option>-d</option></arg>
   <arg choice="plain"><replaceable>oldconfigdir</replaceable></arg>
   <arg choice="plain"><option>-D</option></arg>
   <arg choice="plain"><replaceable>newconfigdir</replaceable></arg>
   <arg rep="repeat"><replaceable>option</replaceable></arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

 <para>
  <application>pg_upgrade</application> (formerly called <application>pg_migrator</application>) allows data
  stored in <productname>PostgreSQL</productname> data files to be upgraded to a later <productname>PostgreSQL</productname>
  major version without the data dump/restore typically required for
  major version upgrades, e.g., from 9.5.8 to 9.6.4 or from 10.7 to 11.2.
  It is not required for minor version upgrades, e.g., from 9.6.2 to 9.6.3
  or from 10.1 to 10.2.
 </para>

 <para>
  Major PostgreSQL releases regularly add new features that often
  change the layout of the system tables, but the internal data storage
  format rarely changes.  <application>pg_upgrade</application> uses this fact
  to perform rapid upgrades by creating new system tables and simply
  reusing the old user data files.  If a future major release ever
  changes the data storage format in a way that makes the old data
  format unreadable, <application>pg_upgrade</application> will not be usable
  for such upgrades.  (The community will attempt to avoid such
  situations.)
 </para>

 <para>
  <application>pg_upgrade</application> does its best to
  make sure the old and new clusters are binary-compatible, e.g.,  by
  checking for compatible compile-time settings, including 32/64-bit
  binaries.  It is important that
  any external modules are also binary compatible, though this cannot
  be checked by <application>pg_upgrade</application>.
 </para>

  <para>
   pg_upgrade supports upgrades from 8.4.X and later to the current
   major release of <productname>PostgreSQL</productname>, including snapshot and beta releases.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    <application>pg_upgrade</application> accepts the following command-line arguments:

    <variablelist>

     <varlistentry>
      <term><option>-b</option> <replaceable>bindir</replaceable></term>
      <term><option>--old-bindir=</option><replaceable>bindir</replaceable></term>
      <listitem><para>the old PostgreSQL executable directory;
      environment variable <envar>PGBINOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-B</option> <replaceable>bindir</replaceable></term>
      <term><option>--new-bindir=</option><replaceable>bindir</replaceable></term>
      <listitem><para>the new PostgreSQL executable directory;
      environment variable <envar>PGBINNEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-c</option></term>
      <term><option>--check</option></term>
      <listitem><para>check clusters only, don't change any data</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-d</option> <replaceable>configdir</replaceable></term>
      <term><option>--old-datadir=</option><replaceable>configdir</replaceable></term>
      <listitem><para>the old database cluster configuration directory; environment
      variable <envar>PGDATAOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-D</option> <replaceable>configdir</replaceable></term>
      <term><option>--new-datadir=</option><replaceable>configdir</replaceable></term>
      <listitem><para>the new database cluster configuration directory; environment
      variable <envar>PGDATANEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-j <replaceable class="parameter">njobs</replaceable></option></term>
      <term><option>--jobs=<replaceable class="parameter">njobs</replaceable></option></term>
      <listitem><para>number of simultaneous processes or threads to use
      </para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-k</option></term>
      <term><option>--link</option></term>
      <listitem><para>use hard links instead of copying files to the new
      cluster</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-o</option> <replaceable class="parameter">options</replaceable></term>
      <term><option>--old-options</option> <replaceable class="parameter">options</replaceable></term>
      <listitem><para>options to be passed directly to the
      old <command>postgres</command> command;  multiple
      option invocations are appended</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-O</option> <replaceable class="parameter">options</replaceable></term>
      <term><option>--new-options</option> <replaceable class="parameter">options</replaceable></term>
      <listitem><para>options to be passed directly to the
      new <command>postgres</command> command;  multiple
      option invocations are appended</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-p</option> <replaceable>port</replaceable></term>
      <term><option>--old-port=</option><replaceable>port</replaceable></term>
      <listitem><para>the old cluster port number; environment
      variable <envar>PGPORTOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-P</option> <replaceable>port</replaceable></term>
      <term><option>--new-port=</option><replaceable>port</replaceable></term>
      <listitem><para>the new cluster port number; environment
      variable <envar>PGPORTNEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-r</option></term>
      <term><option>--retain</option></term>
      <listitem><para>retain SQL and log files even after successful completion
      </para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-U</option> <replaceable>username</replaceable></term>
      <term><option>--username=</option><replaceable>username</replaceable></term>
      <listitem><para>cluster's install user name; environment
      variable <envar>PGUSER</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-v</option></term>
      <term><option>--verbose</option></term>
      <listitem><para>enable verbose internal logging</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-V</option></term>
      <term><option>--version</option></term>
      <listitem><para>display version information, then exit</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-?</option></term>
      <term><option>--help</option></term>
      <listitem><para>show help, then exit</para></listitem>
     </varlistentry>

    </variablelist>
   </para>

 </refsect1>

 <refsect1>
  <title>Usage</title>

  <para>
   These are the steps to perform an upgrade
   with <application>pg_upgrade</application>:
  </para>

  <procedure>
   <step performance="optional">
    <title>Optionally move the old cluster</title>

    <para>
     If you are using a version-specific installation directory, e.g.,
     <filename>/opt/PostgreSQL/&majorversion;</filename>, you do not need to move the old cluster. The
     graphical installers all use version-specific installation directories.
    </para>

    <para>
     If your installation directory is not version-specific, e.g.,
     <filename>/usr/local/pgsql</filename>, it is necessary to move the current PostgreSQL install
     directory so it does not interfere with the new <productname>PostgreSQL</productname> installation.
     Once the current <productname>PostgreSQL</productname> server is shut down, it is safe to rename the
     PostgreSQL installation directory; assuming the old directory is
     <filename>/usr/local/pgsql</filename>, you can do:

<programlisting>
mv /usr/local/pgsql /usr/local/pgsql.old
</programlisting>
     to rename the directory.
    </para>
   </step>

   <step>
    <title>For source installs, build the new version</title>

    <para>
     Build the new PostgreSQL source with <command>configure</command> flags that are compatible
     with the old cluster. <application>pg_upgrade</application> will check <command>pg_controldata</command> to make
     sure all settings are compatible before starting the upgrade.
    </para>
   </step>

   <step>
    <title>Install the new PostgreSQL binaries</title>

    <para>
     Install the new server's binaries and support
     files.  <application>pg_upgrade</application> is included in a default installation.
    </para>

    <para>
     For source installs, if you wish to install the new server in a custom
     location, use the <literal>prefix</literal> variable:

<programlisting>
make prefix=/usr/local/pgsql.new install
</programlisting></para>
   </step>

   <step>
    <title>Initialize the new PostgreSQL cluster</title>

    <para>
     Initialize the new cluster using <command>initdb</command>.
     Again, use compatible <command>initdb</command>
     flags that match the old cluster. Many
     prebuilt installers do this step automatically. There is no need to
     start the new cluster.
    </para>
   </step>

   <step>
    <title>Install extension shared object files</title>

    <para>
     Many extensions and custom modules, whether from
     <filename>contrib</filename> or another source, use shared object
     files (or DLLs), e.g., <filename>pgcrypto.so</filename>.  If the old
     cluster used these, shared object files matching the new server binary
     must be installed in the new cluster, usually via operating system
     commands.  Do not load the schema definitions, e.g., <command>CREATE
     EXTENSION pgcrypto</command>, because these will be duplicated from
     the old cluster.  If extension updates are available,
     <application>pg_upgrade</application> will report this and create
     a script that can be run later to update them.
    </para>
   </step>

   <step>
    <title>Copy custom full-text search files</title>

    <para>
     Copy any custom full text search files (dictionary, synonym,
     thesaurus, stop words) from the old to the new cluster.
    </para>
   </step>

   <step>
    <title>Adjust authentication</title>

    <para>
     <command>pg_upgrade</command> will connect to the old and new servers several
     times, so you might want to set authentication to <literal>peer</literal>
     in <filename>pg_hba.conf</filename> or use a <filename>~/.pgpass</filename> file
     (see <xref linkend="libpq-pgpass"/>).
    </para>
   </step>

   <step>
    <title>Stop both servers</title>

    <para>
     Make sure both database servers are stopped using, on Unix, e.g.:

<programlisting>
pg_ctl -D /opt/PostgreSQL/9.6 stop
pg_ctl -D /opt/PostgreSQL/&majorversion; stop
</programlisting>

     or on Windows, using the proper service names:

<programlisting>
NET STOP postgresql-9.6
NET STOP postgresql-&majorversion;
</programlisting>
    </para>

    <para>
     Streaming replication and log-shipping standby servers can
     remain running until a later step.
    </para>
   </step>

   <step>
    <title>Prepare for standby server upgrades</title>

    <para>
     If you are upgrading standby servers using methods outlined in section <xref
     linkend="pgupgrade-step-replicas"/>, verify that the old standby
     servers are caught up by running <application>pg_controldata</application>
     against the old primary and standby clusters.  Verify that the
     <quote>Latest checkpoint location</quote> values match in all clusters.
     (There will be a mismatch if old standby servers were shut down
     before the old primary or if the old standby servers are still running.)
     Also, make sure <varname>wal_level</varname> is not set to 
     <literal>minimal</literal> in the <filename>postgresql.conf</filename> file on the
     new primary cluster.
    </para>
   </step>

   <step>
    <title>Run <application>pg_upgrade</application></title>

    <para>
     Always run the <application>pg_upgrade</application> binary of the new server, not the old one.
     <application>pg_upgrade</application> requires the specification of the old and new cluster's
     data and executable (<filename>bin</filename>) directories. You can also specify
     user and port values, and whether you want the data files linked
     instead of the default copy behavior.
    </para>

    <para>
     If you use link mode, the upgrade will be much faster (no file
     copying) and use less disk space, but you will not be able to access
     your old cluster
     once you start the new cluster after the upgrade.  Link mode also
     requires that the old and new cluster data directories be in the
     same file system.  (Tablespaces and <filename>pg_wal</filename> can be on
     different file systems.)  See <literal>pg_upgrade --help</literal> for a full
     list of options.
    </para>

    <para>
     The <option>--jobs</option> option allows multiple CPU cores to be used
     for copying/linking of files and to dump and restore database schemas
     in parallel;  a good place to start is the maximum of the number of
     CPU cores and tablespaces.  This option can dramatically reduce the
     time to upgrade a multi-database server running on a multiprocessor
     machine.
    </para>

    <para>
     For Windows users, you must be logged into an administrative account, and
     then start a shell as the <literal>postgres</literal> user and set the proper path:

<programlisting>
RUNAS /USER:postgres "CMD.EXE"
SET PATH=%PATH%;C:\Program Files\PostgreSQL\&majorversion;\bin;
</programlisting>

     and then run <application>pg_upgrade</application> with quoted directories, e.g.:

<programlisting>
pg_upgrade.exe
        --old-datadir "C:/Program Files/PostgreSQL/9.6/data"
        --new-datadir "C:/Program Files/PostgreSQL/&majorversion;/data"
        --old-bindir "C:/Program Files/PostgreSQL/9.6/bin"
        --new-bindir "C:/Program Files/PostgreSQL/&majorversion;/bin"
</programlisting>

     Once started, <command>pg_upgrade</command> will verify the two clusters are compatible
     and then do the upgrade. You can use <command>pg_upgrade --check</command>
     to perform only the checks, even if the old server is still
     running. <command>pg_upgrade --check</command> will also outline any
     manual adjustments you will need to make after the upgrade.  If you
     are going to be using link mode, you should use the <option>--link</option>
     option with <option>--check</option> to enable link-mode-specific checks.
     <command>pg_upgrade</command> requires write permission in the current directory.
    </para>

    <para>
     Obviously, no one should be accessing the clusters during the
     upgrade.  <application>pg_upgrade</application> defaults to running servers
     on port 50432 to avoid unintended client connections.
     You can use the same port number for both clusters when doing an
     upgrade because the old and new clusters will not be running at the
     same time.  However, when checking an old running server, the old
     and new port numbers must be different.
    </para>

    <para>
     If an error occurs while restoring the database schema, <command>pg_upgrade</command> will
     exit and you will have to revert to the old cluster as outlined in <xref linkend="pgupgrade-step-revert"/>
     below. To try <command>pg_upgrade</command> again, you will need to modify the old
     cluster so the pg_upgrade schema restore succeeds. If the problem is a
     <filename>contrib</filename> module, you might need to uninstall the <filename>contrib</filename> module from
     the old cluster and install it in the new cluster after the upgrade,
     assuming the module is not being used to store user data.
    </para>
   </step>

   <step id="pgupgrade-step-replicas">
    <title>Upgrade Streaming Replication and Log-Shipping standby servers</title>

    <para>
     If you used link mode and have Streaming Replication (see <xref
     linkend="streaming-replication"/>) or Log-Shipping (see <xref
     linkend="warm-standby"/>) standby servers, you can follow these steps to
     quickly upgrade them.  You will not be running <application>pg_upgrade</application> on
     the standby servers, but rather <application>rsync</application> on the primary.
     Do not start any servers yet.
    </para>

    <para>
     If you did <emphasis>not</emphasis> use link mode, do not have or do not
     want to use <application>rsync</application>, or want an easier solution, skip
     the instructions in this section and simply recreate the standby
     servers once <application>pg_upgrade</application> completes and the new primary
     is running.
    </para>

    <substeps>

     <step>
      <title>Install the new PostgreSQL binaries on standby servers</title>

      <para>
       Make sure the new binaries and support files are installed on all
       standby servers.
      </para>
     </step>

     <step>
      <title>Make sure the new standby data directories do <emphasis>not</emphasis> exist</title>

      <para>
       Make sure the new standby data directories do <emphasis>not</emphasis>
       exist or are empty.  If <application>initdb</application> was run, delete
       the standby servers' new data directories.
      </para>
     </step>

     <step>
      <title>Install extension shared object files</title>

      <para>
       Install the same extension shared object files on the new standbys
       that you installed in the new primary cluster.
      </para>
     </step>

     <step>
      <title>Stop standby servers</title>

      <para>
       If the standby servers are still running, stop them now using the
       above instructions.
      </para>
     </step>

     <step>
      <title>Save configuration files</title>

      <para>
       Save any configuration files from the old standbys' configuration
       directories you need to keep, e.g.,  <filename>postgresql.conf</filename>
       (and any files included by it), <filename>postgresql.auto.conf</filename>,
       <literal>recovery.conf</literal>, <literal>pg_hba.conf</literal>,
       because these will be overwritten or removed in the next step.
      </para>
     </step>

     <step>
      <title>Run <application>rsync</application></title>

      <para>
       When using link mode, standby servers can be quickly upgraded using
       <application>rsync</application>.  To accomplish this, from a directory on
       the primary server that is above the old and new database cluster
       directories, run this on the <emphasis>primary</emphasis> for each standby
       server:

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive old_cluster new_cluster remote_dir
</programlisting>

       where <option>old_cluster</option> and <option>new_cluster</option> are relative
       to the current directory on the primary, and <option>remote_dir</option>
       is <emphasis>above</emphasis> the old and new cluster directories
       on the standby.  The directory structure under the specified
       directories on the primary and standbys must match.  Consult the
       <application>rsync</application> manual page for details on specifying the
       remote directory, e.g.,

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive /opt/PostgreSQL/9.5 \
      /opt/PostgreSQL/9.6 standby.example.com:/opt/PostgreSQL
</programlisting>

       You can verify what the command will do using
       <application>rsync</application>'s <option>--dry-run</option> option.  While
       <application>rsync</application> must be run on the primary for at least one
       standby, it is possible to run <application>rsync</application> on an upgraded
       standby to upgrade other standbys, as long as the upgraded standby
       has not been started.
      </para>

      <para>
       What this does is to record the links created by
       <application>pg_upgrade</application>'s link mode that connect files in the
       old and new clusters on the primary server.  It then finds matching
       files in the standby's old cluster and creates links for them in the
       standby's new cluster.  Files that were not linked on the primary
       are copied from the primary to the standby.  (They are usually
       small.)  This provides rapid standby upgrades.  Unfortunately,
       <application>rsync</application> needlessly copies files associated with
       temporary and unlogged tables because these files don't normally
       exist on standby servers.
      </para>

      <para>
       If you have tablespaces, you will need to run a similar
       <application>rsync</application> command for each tablespace directory, e.g.:

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tblsp/PG_9.5_201510051 \
      /vol1/pg_tblsp/PG_9.6_201608131 standby.example.com:/vol1/pg_tblsp
</programlisting>

       If you have relocated <filename>pg_wal</filename> outside the data
       directories, <application>rsync</application> must be run on those directories
       too.
      </para>
     </step>

     <step>
      <title>Configure streaming replication and log-shipping standby servers</title>

      <para>
       Configure the servers for log shipping.  (You do not need to run
       <function>pg_start_backup()</function> and <function>pg_stop_backup()</function>
       or take a file system backup as the standbys are still synchronized
       with the primary.)  Replication slots are not copied and must
       be recreated.
      </para>
     </step>

    </substeps>

   </step>

   <step>
    <title>Restore <filename>pg_hba.conf</filename></title>

    <para>
     If you modified <filename>pg_hba.conf</filename>, restore its original settings.
     It might also be necessary to adjust other configuration files in the new
     cluster to match the old cluster, e.g., <filename>postgresql.conf</filename>
     (and any files included by it), <filename>postgresql.auto.conf</filename>.
    </para>
   </step>

   <step>
    <title>Start the new server</title>

    <para>
     The new server can now be safely started, and then any
     <application>rsync</application>'ed standby servers.
    </para>
   </step>

   <step>
    <title>Post-Upgrade processing</title>

    <para>
     If any post-upgrade processing is required, pg_upgrade will issue
     warnings as it completes. It will also generate script files that must
     be run by the administrator. The script files will connect to each
     database that needs post-upgrade processing. Each script should be
     run using:

<programlisting>
psql --username=postgres --file=script.sql postgres
</programlisting>

     The scripts can be run in any order and can be deleted once they have
     been run.
    </para>

    <caution>
    <para>
     In general it is unsafe to access tables referenced in rebuild scripts
     until the rebuild scripts have run to completion; doing so could yield
     incorrect results or poor performance. Tables not referenced in rebuild
     scripts can be accessed immediately.
    </para>
    </caution>
   </step>

   <step>
    <title>Statistics</title>

    <para>
     Because optimizer statistics are not transferred by <command>pg_upgrade</command>, you will
     be instructed to run a command to regenerate that information at the end
     of the upgrade.  You might need to set connection parameters to
     match your new cluster.
    </para>
   </step>

   <step>
    <title>Delete old cluster</title>

    <para>
     Once you are satisfied with the upgrade, you can delete the old
     cluster's data directories by running the script mentioned when
     <command>pg_upgrade</command> completes. (Automatic deletion is not
     possible if you have user-defined tablespaces inside the old data
     directory.)  You can also delete the old installation directories
     (e.g., <filename>bin</filename>, <filename>share</filename>).
    </para>
   </step>

   <step id="pgupgrade-step-revert" performance="optional">
    <title>Reverting to old cluster</title>

    <para>
     If, after running <command>pg_upgrade</command>, you wish to revert to the old cluster,
     there are several options:

     <itemizedlist>
      <listitem>
       <para>
        If the <option>--check</option> option was used, the old cluster
        was unmodified;  it can be restarted.
       </para>
      </listitem>

      <listitem>
       <para>
        If the <option>--link</option> option was <emphasis>not</emphasis>
        used, the old cluster was unmodified;  it can be restarted.
       </para>
      </listitem>

      <listitem>
       <para>
        If the <option>--link</option> option was used, the data
        files might be shared between the old and new cluster:

        <itemizedlist>
         <listitem>
          <para>
           If <command>pg_upgrade</command> aborted before linking started,
           the old cluster was unmodified;  it can be restarted.
          </para>
         </listitem>

         <listitem>
          <para>
           If you did <emphasis>not</emphasis> start the new cluster, the old
           cluster was unmodified except that, when linking started, a
           <literal>.old</literal> suffix was appended to
           <filename>$PGDATA/global/pg_control</filename>.  To reuse the old
           cluster, remove the <filename>.old</filename> suffix from
           <filename>$PGDATA/global/pg_control</filename>; you can then restart
           the old cluster.
          </para>
         </listitem>

         <listitem>
          <para>
           If you did start the new cluster, it has written to shared files
           and it is unsafe to use the old cluster.  The old cluster will
           need to be restored from backup in this case.
          </para>
         </listitem>

        </itemizedlist>
       </para>
      </listitem>
     </itemizedlist>
    </para>
   </step>
  </procedure>

 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <application>pg_upgrade</application> does not support upgrading of databases
   containing table columns using these <type>reg*</type> OID-referencing system data types:
   <type>regproc</type>, <type>regprocedure</type>, <type>regoper</type>,
   <type>regoperator</type>, <type>regconfig</type>, and
   <type>regdictionary</type>.  (<type>regtype</type> can be upgraded.)
  </para>

  <para>
   All failure, rebuild, and reindex cases will be reported by
   <application>pg_upgrade</application> if they affect your installation;
   post-upgrade scripts to rebuild tables and indexes will be
   generated automatically.  If you are trying to automate the upgrade
   of many clusters, you should find that clusters with identical database
   schemas require the same post-upgrade steps for all cluster upgrades;
   this is because the post-upgrade steps are based on the database
   schemas, and not user data.
  </para>

  <para>
   For deployment testing, create a schema-only copy of the old cluster,
   insert dummy data, and upgrade that.
  </para>

  <para>
   If you are upgrading a pre-<productname>PostgreSQL</productname> 9.2 cluster
   that uses a configuration-file-only directory, you must pass the
   real data directory location to <application>pg_upgrade</application>, and
   pass the configuration directory location to the server, e.g.,
   <literal>-d /real-data-directory -o '-D /configuration-directory'</literal>.
  </para>

  <para>
   If using a pre-9.1 old server that is using a non-default Unix-domain
   socket directory or a default that differs from the default of the
   new cluster, set <envar>PGHOST</envar> to point to the old server's socket
   location.  (This is not relevant on Windows.)
  </para>

  <para>
   If you want to use link mode and you do not want your old cluster
   to be modified when the new cluster is started, make a copy of the
   old cluster and upgrade that in link mode. To make a valid copy
   of the old cluster, use <command>rsync</command> to create a dirty
   copy of the old cluster while the server is running, then shut down
   the old server and run <command>rsync --checksum</command> again to update the
   copy with any changes to make it consistent.  (<option>--checksum</option>
   is necessary because <command>rsync</command> only has file modification-time
   granularity of one second.)  You might want to exclude some
   files, e.g., <filename>postmaster.pid</filename>, as documented in <xref
   linkend="backup-lowlevel-base-backup"/>.  If your file system supports
   file system snapshots or copy-on-write file copies, you can use that
   to make a backup of the old cluster and tablespaces, though the snapshot
   and copies must be created simultaneously or while the database server
   is down.
  </para>

 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="app-initdb"/></member>
   <member><xref linkend="app-pg-ctl"/></member>
   <member><xref linkend="app-pgdump"/></member>
   <member><xref linkend="app-postgres"/></member>
  </simplelist>
 </refsect1>
</refentry>
