<!-- doc/src/sgml/runtime.sgml -->

<chapter id="runtime">
 <title>Server Setup and Operation</title>

 <para>
  This chapter discusses how to set up and run the database server,
  and its interactions with the operating system.
 </para>

 <para>
  The directions in this chapter assume that you are working with
  plain <productname>PostgreSQL</productname> without any additional
  infrastructure, for example a copy that you built from source
  according to the directions in the preceding chapters.
  If you are working with a pre-packaged or vendor-supplied
  version of <productname>PostgreSQL</productname>, it is likely that
  the packager has made special provisions for installing and starting
  the database server according to your system's conventions.
  Consult the package-level documentation for details.
 </para>

 <sect1 id="postgres-user">
  <title>The <productname>PostgreSQL</productname> User Account</title>

  <indexterm>
   <primary>postgres user</primary>
  </indexterm>

  <para>
   As with any server daemon that is accessible to the outside world,
   it is advisable to run <productname>PostgreSQL</productname> under a
   separate user account. This user account should only own the data
   that is managed by the server, and should not be shared with other
   daemons. (For example, using the user <literal>nobody</literal> is a bad
   idea.) In particular, it is advisable that this user account not own
   the <productname>PostgreSQL</productname> executable files, to ensure
   that a compromised server process could not modify those executables.
  </para>

  <para>
   Pre-packaged versions of <productname>PostgreSQL</productname> will
   typically create a suitable user account automatically during
   package installation.
  </para>

  <para>
   To add a Unix user account to your system, look for a command
   <command>useradd</command> or <command>adduser</command>. The user
   name <systemitem>postgres</systemitem> is often used, and is assumed
   throughout this book, but you can use another name if you like.
  </para>
 </sect1>

 <sect1 id="creating-cluster">
  <title>Creating a Database Cluster</title>

  <indexterm>
   <primary>database cluster</primary>
  </indexterm>

  <indexterm>
   <primary>data area</primary>
   <see>database cluster</see>
  </indexterm>

  <para>
   Before you can do anything, you must initialize a database storage
   area on disk. We call this a <firstterm>database cluster</firstterm>.
   (The <acronym>SQL</acronym> standard 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 <literal>postgres</literal>,
   which is meant as a default database for use by utilities, users and third
   party applications.  The database server itself does not require the
   <literal>postgres</literal> database to exist, but many external utility
   programs assume it exists.  There 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>