are two more databases created within
   each cluster during initialization, named <literal>template1</literal>
   and <literal>template0</literal>.  As the names suggest, these will be
   used as templates for subsequently-created databases; they should not be
   used for actual work.  (See <xref linkend="managing-databases"/> for
   information about creating new databases within a cluster.)
  </para>

  <para>
   In file system terms, a database cluster is a single directory
   under which all data will be stored. We call this the <firstterm>data
   directory</firstterm> or <firstterm>data area</firstterm>. It is
   completely up to you where you choose to store your data.  There is no
   default, although locations such as
   <filename>/usr/local/pgsql/data</filename> or
   <filename>/var/lib/pgsql/data</filename> are popular.
   The data directory must be initialized before being used, using the program
   <xref linkend="app-initdb"/><indexterm><primary>initdb</primary></indexterm>
   which is installed with <productname>PostgreSQL</productname>.
  </para>

  <para>
   If you are using a pre-packaged version
   of <productname>PostgreSQL</productname>, it may well have a specific
   convention for where to place the data directory, and it may also
   provide a script for creating the data directory.  In that case you
   should use that script in preference to
   running <command>initdb</command> directly.
   Consult the package-level documentation for details.
  </para>

  <para>
   To initialize a database cluster manually,
   run <command>initdb</command> and specify the desired
   file system location of the database cluster with the
   <option>-D</option> option, for example:
<screen>
<prompt>$</prompt> <userinput>initdb -D /usr/local/pgsql/data</userinput>
</screen>
   Note that you must execute this command while logged into the
   <productname>PostgreSQL</productname> user account, which is
   described in the previous section.
  </para>

  <tip>
   <para>
    As an alternative to the <option>-D</option> option, you can set
    the environment variable <envar>PGDATA</envar>.
    <indexterm><primary><envar>PGDATA</envar></primary></indexterm>
   </para>
  </tip>

  <para>
   Alternatively, you can run <command>initdb</command> via
   the <xref linkend="app-pg-ctl"/>
   program<indexterm><primary>pg_ctl</primary></indexterm> like so:
<screen>
<prompt>$</prompt> <userinput>pg_ctl -D /usr/local/pgsql/data initdb</userinput>
</screen>
   This may be more intuitive if you are
   using <command>pg_ctl</command> for starting and stopping the
   server (see <xref linkend="server-start"/>), so
   that <command>pg_ctl</command> would be the sole command you use
   for managing the database server instance.
  </para>

  <para>
   <command>initdb</command> will attempt to create the directory you
   specify if it does not already exist.  Of course, this will fail if
   <command>initdb</command> does not have permissions to write in the
   parent directory.  It's generally recommendable that the
   <productname>PostgreSQL</productname> user own not just the data
   directory but its parent directory as well, so that this should not
   be a problem.  If the desired parent directory doesn't exist either,
   you will need to create it first, using root privileges if the
   grandparent directory isn't writable.  So the process might look
   like this:
<screen>
root# <userinput>mkdir /usr/local/pgsql</userinput>
root# <userinput>chown postgres /usr/local/pgsql</userinput>
root# <userinput>su postgres</userinput>
postgres$ <userinput>initdb -D /usr/local/pgsql/data</userinput>
</screen>
  </para>

  <para>
   <command>initdb</command> will refuse to run if the data directory
   exists and already contains files; this is to prevent accidentally
   overwriting an existing installation.
  </para>

  <para>
   Because the data directory contains all the data stored in the
   database, it is essential that it be secured from unauthorized