Neos\Flow\Core\Booting\Scripts::initializeSystemLogger PHP Method

    public static function initializeSystemLogger(Bootstrap $bootstrap)
    {
        $configurationManager = $bootstrap->getEarlyInstance(ConfigurationManager::class);
        $settings = $configurationManager->getConfiguration(ConfigurationManager::CONFIGURATION_TYPE_SETTINGS, 'Neos.Flow');
        if (!isset($settings['log']['systemLogger']['logger'])) {
            $settings['log']['systemLogger']['logger'] = Logger::class;
        }
        $loggerFactory = new LoggerFactory();
        $bootstrap->setEarlyInstance(LoggerFactory::class, $loggerFactory);
        $systemLogger = $loggerFactory->create('SystemLogger', $settings['log']['systemLogger']['logger'], $settings['log']['systemLogger']['backend'], $settings['log']['systemLogger']['backendOptions']);
        $bootstrap->setEarlyInstance(SystemLoggerInterface::class, $systemLogger);
    }