Understanding the directory structure of a default Drupal installation will teach you several important best practices, such as where downloaded modules and themes should reside and how to have different Drupal installation profiles. A default Drupal installation has the structure shown:
The default folder structure of a Drupal installation
Details about each element in the folder structure follow:
• The includes folder contains libraries of common functions that Drupal uses.
• The modules folder contains the core modules, with each module in its own folder. It is best not to touch anything in this folder (or any other folder except profiles and sites). You add extra modules in the sites directory.
• The profiles folder contains different installation profiles for a site. If there are other profiles besides the default profile in this subdirectory, Drupal will ask you which profile you want to install when first installing your Drupal site. The main purpose of an installation profile is to enable certain core and contributed modules automatically. An example would be an e-commerce profile that automatically sets up Drupal as an e-commerce platform.
• The scripts folder contains scripts for checking syntax, cleaning up code, running Drupal from the command line, handling special cases with cron, and running the test suites (new in Drupal 7). This folder is not used within the Drupal request life cycle; these are shell and Perl utility scripts.
• The sites directory (see Figure Sites Directory below) contains your modifications to Drupal in the form of settings, modules, and themes. When you add modules to Drupal from the contributed modules repository or by writing your own, they go into -sites/all/modules. This keeps all your Drupal modifications within a single folder. Inside the sites directory will be a subdirectory named default that holds the default configuration file for your Drupal site—default.settings.php. The Drupal installer will modify these original settings based on the information you provide and write a settings.php file for your site. The default directory is typically copied and renamed to the URL of your site by the person deploying the site, so your final settings file would be at sites/www.example.com/settings.php.
• The sites/default/files folder is included in the base installation of Drupal by default. It is needed to store any files that are uploaded to your site and subsequently served out. Some examples are the use of a custom logo, enabling user avatars, or uploading other media associated with your new site. This subdirectory requires read and write permissions by the web server that Drupal is running behind. Drupal’s installer will create this subdirectory if it can and will check that the correct permissions have been set. In addition to sites/default/files, a sites/default/private directory may be created for storing files that are sensitive in nature and shouldn’t be displayed unless the site visitor has the proper credentials. You create the private files directory by
navigating to Configuration > File System and entering the directory where you want private files to reside in the text field titled Private file system path.
• The themes folder contains the template engines and default themes for Drupal. Additional themes you download or create should not go here; they go into sites/all/themes.
• cron.php is used for executing periodic tasks, such as pruning database tables and calculating statistics.
• index.php is the main entry point for serving requests.
• install.php is the main entry point for the Drupal installer.
• update.php updates the database schema after a Drupal version upgrade.
• xmlrpc.php receives XML-RPC requests and may be safely deleted from deployments that do not intend to receive XML-RPC requests.
• robots.txt is a default implementation of the robot exclusion standard.
• authorize.php is an administrative script for running authorized file operations— for example, downloading an installing a new theme or module from Drupal.org.
The sites folder can store all your Drupal modifications.
(configuration, themes, modules & files etc.)
Note: While taking sites backups, all you need is to just backup the sites directory (and the directory that stores files uploaded, if its not sites/default/files or if it is not inside sites folder).