System configuration files

config/system/settings.php

settings.php
Scope
project
Path (Composer)
config/system/settings.php
Path (Classic)
typo3conf/system/settings.php

The most important configuration file is settings.php. It contains local settings of the main global PHP array $GLOBALS['TYPO3_CONF_VARS'] , crucial settings like database connect credentials are in here. The file is managed by the modules in section Admin Tools.

config/system/additional.php

additional.php
Scope
project
Path (Composer)
config/system/additional.php
Path (Classic)
typo3conf/system/additional.php

The settings in the settings.php can be overridden in the additional.php file, which is never touched by TYPO3 internal management tools. Be aware that having settings within additional.php may prevent the system from performing automatic upgrades and should be used with care and only if you know what you are doing.

The configuration files settings.php and additional.php are located in the directory config/system/ in Composer-based installations. In classic installations they are located in typo3conf/system/.

This path can be retrieved from the Environment API, see getConfigPath() for both Composer-based and classic installations.