To initialize a database cluster, use the command initdb, which is installed with PostgreSQL. There is no default, although locations such as /usr/local/pgsql/data or /var/lib/pgsql/data are popular. It is completely up to you where you choose to store your data. We call this the data directory or data area. In file system terms, a database cluster is a single directory under which all data will be stored. (See Chapter 21 for information about creating new databases within a cluster.) As the name suggests, this will be used as a template for subsequently created databases it should not be used for actual work. Another database created within each cluster during initialization is called template1. The database server itself does not require the postgres database to exist, but many external utility programs assume it exists. After initialization, a database cluster will contain a database named postgres, which is meant as a default database for use by utilities, users and third party applications. (The SQL 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. Before you can do anything, you must initialize a database storage area on disk.
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