The LocalConfiguration.php file

The global configuration is stored in file typo3conf/LocalConfiguration.php.

Important

Since configuration settings can be manipulated from within the TYPO3 CMS backend, the typo3conf/LocalConfiguration.php must be writable by the web server user.

The local configuration file is basically a long array which is simply returned when the file is included. It represents the global TYPO3 CMS configuration. This configuration can be modified/extended/overridden by extensions, by setting configuration options inside an extension’s ext_localconf.php file. See Core APIs for more details about extension structure.

Here is the local configuration file after the basic installation:

<?php
return [
        'BE' => [
                'debug' => true,
                'explicitADmode' => 'explicitAllow',
                'installToolPassword' => '$P$Cbp90UttdtIKELNrDGjy4tDxh3uu9D/',
                'loginSecurityLevel' => 'rsa',
        ],
        'DB' => [
                'database' => 'empty_typo3',
                'host' => 'localhost',
                'password' => 'foo',
                'socket' => '',
                'username' => 'bar',
        ],
        'EXT' => [
                'extConf' => [
                        'css_styled_content' => 'a:1:{s:32:"loadContentElementWizardTsConfig";s:1:"1";}',
                        'doc_tut_templating' => 'a:0:{}',
                        'rsaauth' => 'a:1:{s:18:"temporaryDirectory";s:0:"";}',
                        'saltedpasswords' => 'a:2:{s:3:"BE.";a:4:{s:21:"saltedPWHashingMethod";s:41:"TYPO3\\CMS\\Saltedpasswords\\Salt\\PhpassSalt";s:11:"forceSalted";i:0;s:15:"onlyAuthService";i:0;s:12:"updatePasswd";i:1;}s:3:"FE.";a:5:{s:7:"enabled";i:1;s:21:"saltedPWHashingMethod";s:41:"TYPO3\\CMS\\Saltedpasswords\\Salt\\PhpassSalt";s:11:"forceSalted";i:0;s:15:"onlyAuthService";i:0;s:12:"updatePasswd";i:1;}}',
                        't3editor' => 'a:0:{}',
                ],
        ],
        'FE' => [
                'debug' => true,
                'loginSecurityLevel' => 'rsa',
        ],
        'GFX' => [
                'colorspace' => 'RGB',
                'im' => 1,
                'im_mask_temp_ext_gif' => 1,
                'im_path' => '/usr/local/bin/',
                'im_path_lzw' => '/usr/local/bin/',
                'im_v5effects' => -1,
                'im_version_5' => 'gm',
                'image_processing' => 1,
                'jpg_quality' => '80',
        ],
        'INSTALL' => [
                'wizardDone' => [
                        'TYPO3\CMS\Install\Updates\AccessRightParametersUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\BackendUserStartModuleUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\Compatibility6ExtractionUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\ContentTypesToTextMediaUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\ExtensionManagerTables' => 1,
                        'TYPO3\CMS\Install\Updates\FileListIsStartModuleUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\FilesReplacePermissionUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\LanguageIsoCodeUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\MediaceExtractionUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\MigrateMediaToAssetsForTextMediaCe' => 1,
                        'TYPO3\CMS\Install\Updates\MigrateShortcutUrlsAgainUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\OpenidExtractionUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\PageShortcutParentUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\ProcessedFileChecksumUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\TableFlexFormToTtContentFieldsUpdate' => 1,
                        'TYPO3\CMS\Install\Updates\WorkspacesNotificationSettingsUpdate' => 1,
                        'TYPO3\CMS\Rtehtmlarea\Hook\Install\DeprecatedRteProperties' => 1,
                        'TYPO3\CMS\Rtehtmlarea\Hook\Install\RteAcronymButtonRenamedToAbbreviation' => 1,
                ],
        ],
        'MAIL' => [
                'transport_sendmail_command' => '/usr/sbin/sendmail -t -i ',
        ],
        'SYS' => [
                'caching' => [
                        'cacheConfigurations' => [
                                'extbase_object' => [
                                        'backend' => 'TYPO3\\CMS\\Core\\Cache\\Backend\\Typo3DatabaseBackend',
                                        'frontend' => 'TYPO3\\CMS\\Core\\Cache\\Frontend\\VariableFrontend',
                                        'groups' => [
                                                'system',
                                        ],
                                        'options' => [
                                                'defaultLifetime' => 0,
                                        ],
                                ],
                        ],
                ],
                'clearCacheSystem' => true,
                'devIPmask' => '*',
                'displayErrors' => 1,
                'enableDeprecationLog' => 'file',
                'encryptionKey' => '0396e1b6b53bf48b0bfed9e97a62744158452dfb9b9909fe32d4b7a709816c9b4e94dcd69c011f989d322cb22309f2f2',
                'exceptionalErrors' => 28674,
                'isInitialDatabaseImportDone' => true,
                'isInitialInstallationInProgress' => false,
                'sitename' => 'New TYPO3 site',
                'sqlDebug' => 1,
                'systemLogLevel' => 0,
                't3lib_cs_convMethod' => 'mbstring',
                't3lib_cs_utils' => 'mbstring',
        ],
];

As you can see, the array is structured on two main levels. The first level corresponds roughly to a category, the second one being properties, which may themselves be arrays.

The configuration categories are:

BE
Options related to the TYPO3 CMS backend
DB
Database connection configuration
EXT
Extension configuration options. The settings of each extension is stored as a serialized array.
FE
Frontend-related options.
GFX
Options related to image manipulation.
INSTALL
The Install Tool does not have any options, but stores in the local configuration file the list of upgrade wizards that were already executed (to avoid presenting them to the user over and over again).
MAIL
Options related to the sending of emails (transport, server, etc.).
SYS
General options which may affect both the frontend and the backend.

Details on the various configuration-options can be found in the install-tool as well as the TYPO3-source at typo3/sysext/core/Configuration/DefaultConfiguration.php. The documentation shown in the install-tool is automatically extracted from those comments of DefaultConfiguration.php.