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><H1
CLASS="SECT1"
><A
NAME="CREATING-CLUSTER"
>17.2. Creating a Database Cluster</A
></H1
><A
NAME="AEN23514"
></A
><A
NAME="AEN23516"
></A
><P
>   Before you can do anything, you must initialize a database storage
   area on disk. We call this a <I
CLASS="FIRSTTERM"
>database cluster</I
>.
   (<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> uses the term catalog cluster.) A
   database cluster is a collection of databases that is managed by a
   single instance of a running database server. After initialization, a
   database cluster will contain a database named <TT
CLASS="LITERAL"
>postgres</TT
>,
   which is meant as a default database for use by utilities, users and third
   party applications.  The database server itself does not require the
   <TT
CLASS="LITERAL"
>postgres</TT
> database to exist, but many external utility
   programs assume it exists.  Another database created within each cluster
   during initialization is called
   <TT
CLASS="LITERAL"
>template1</TT
>.  As the name suggests, this will be used
   as a template for subsequently created databases; it should not be
   used for actual work.  (See <A
HREF="managing-databases.html"
>Chapter 21</A
> for
   information about creating new databases within a cluster.)
  </P
><P
>   In file system terms, a database cluster will be a single directory
   under which all data will be stored. We call this the <I
CLASS="FIRSTTERM"
>data
   directory</I
> or <I
CLASS="FIRSTTERM"
>data area</I
>. It is
   completely up to you where you choose to store your data.  There is no
   default, although locations such as
   <TT
CLASS="FILENAME"
>/usr/local/pgsql/data</TT
> or
   <TT
CLASS="FILENAME"
>/var/lib/pgsql/data</TT
> are popular. To initialize a
   database cluster, use the command <A
HREF="app-initdb.html"
>initdb</A
>,<A
NAME="AEN23532"
></A
> which is
   installed with <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>. The desired
   file system location of your database cluster is indicated by the
   <TT
CLASS="OPTION"
>-D</TT
> option, for example:
</P><PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>$</SAMP
> <KBD
CLASS="USERINPUT"
>initdb -D /usr/local/pgsql/data</KBD
></PRE
><P>
   Note that you must execute this command while logged into the
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user account, which is
   described in the previous section.
  </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>    As an alternative to the <TT
CLASS="OPTION"
>-D</TT
> option, you can set
    the environment variable <TT
CLASS="ENVAR"
>PGDATA</TT
>.
    <A
NAME="AEN23544"
></A
>
   </P
></BLOCKQUOTE
></DIV
><P
>   <TT
CLASS="COMMAND"
>initdb</TT
> will attempt to create the directory you
   specify if it does not already exist. It is likely that it will not
   have the permission to do so (if you followed our advice and created
   an unprivileged account). In that case you should create the
   directory yourself (as root) and change the owner to be the
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user. Here is how this might
   be done:
</P><PRE
CLASS="SCREEN"
>root# <KBD
CLASS="USERINPUT"
>mkdir /usr/local/pgsql/data</KBD
>
root# <KBD
CLASS="USERINPUT"
>chown postgres /usr/local/pgsql/data</KBD
>
root# <KBD
CLASS="USERINPUT"
>su postgres</KBD
>
postgres$ <KBD
CLASS="USERINPUT"
>initdb -D /usr/local/pgsql/data</KBD
></PRE
><P>
  </P
><P
>   <TT
CLASS="COMMAND"
>initdb</TT
> will refuse to run if the data directory
   looks like it has already been initialized.</P
><P
>   Because the data directory contains all the data stored in the
   database, it is essential that it be secured from unauthorized
   access. <TT
CLASS="COMMAND"
>initdb</TT
> therefore revokes access
   permissions from everyone but the
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user.
  </P
><P
>   However, while the directory contents are secure, the default
   client authentication setup allows any local user to connect to the
   database and even become the database superuser. If you do not
   trust other local users, we recommend you use one of
   <TT
CLASS="COMMAND"
>initdb</TT
>'s <TT
CLASS="OPTION"
>-W</TT
>, <TT
CLASS="OPTION"
>--pwprompt</TT
>
   or <TT
CLASS="OPTION"
>--pwfile</TT
> options to assign a password to the
   database superuser.<A
NAME="AEN23565"
></A
>  Also, specify <TT
CLASS="OPTION"
>-A md5</TT
> or
   <TT
CLASS="OPTION"
>-A password</TT
> so that the default <TT
CLASS="LITERAL"
>trust</TT
> authentication
   mode is not used; or modify the generated <TT
CLASS="FILENAME"
>pg_hba.conf</TT
>
   file after running <TT
CLASS="COMMAND"
>initdb</TT
>,
   <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>before</I
></SPAN
> you start the server for the first time. (Other
   reasonable approaches include using <TT
CLASS="LITERAL"
>ident</TT
> authentication
   or file system permissions to restrict connections. See <A
HREF="client-authentication.html"
>Chapter 19</A
> for more information.)
  </P
><P
>   <TT
CLASS="COMMAND"
>initdb</TT
> also initializes the default
   locale<A
NAME="AEN23578"
></A
> for the database cluster.
   Normally, it will just take the locale settings in the environment
   and apply them to the initialized database.  It is possible to
   specify a different locale for the database; more information about
   that can be found in <A
HREF="locale.html"
>Section 22.1</A
>.  The default sort order used
   within the particular database cluster is set by
   <TT
CLASS="COMMAND"
>initdb</TT
>, and while you can create new databases using
   different sort order, the order used in the template databases that initdb
   creates cannot be changed without dropping and recreating them.
   There is also a performance impact for using locales
   other than <TT
CLASS="LITERAL"
>C</TT
> or <TT
CLASS="LITERAL"
>POSIX</TT
>. Therefore, it is
   important to make this choice correctly the first time.
  </P
><P
>   <TT
CLASS="COMMAND"
>initdb</TT
> also sets the default character set encoding
   for the database cluster.  Normally this should be chosen to match the
   locale setting.  For details see <A
HREF="multibyte.html"
>Section 22.2</A
>.
  </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CREATING-CLUSTER-NFS"
>17.2.1. Network File Systems</A
></H2
><A
NAME="AEN23589"
></A
><A
NAME="AEN23591"
></A
><A
NAME="AEN23595"
></A
><P
>    Many installations create database clusters on network file systems.
    Sometimes this is done directly via <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
>, or by using a
    Network Attached Storage (<ACRONYM
CLASS="ACRONYM"
>NAS</ACRONYM
>) device that uses
    <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> internally.  <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does nothing
    special for <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> file systems, meaning it assumes
    <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> behaves exactly like locally-connected drives
    (<ACRONYM
CLASS="ACRONYM"
>DAS</ACRONYM
>, Direct Attached Storage).  If client and server
    <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> implementations have non-standard semantics, this can
    cause reliability problems (see <A
HREF="http://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
TARGET="_top"
>http://www.time-travellers.org/shane/papers/NFS_considered_harmful.html</A
>).
    Specifically, delayed (asynchronous) writes to the <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
>
    server can cause reliability problems;   if possible, mount
    <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> file systems synchronously (without caching) to avoid
    this.  Also, soft-mounting <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
> is not recommended.
    (Storage Area Networks (<ACRONYM
CLASS="ACRONYM"
>SAN</ACRONYM
>) use a low-level
    communication protocol rather than <ACRONYM
CLASS="ACRONYM"
>NFS</ACRONYM
>.)
   </P
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