Check Apache/Nginx error logs: ```bash # Apache tail -n 50 /var/log/apache2/error.log # Nginx tail -n 50 /var/log/nginx/error.log ``` Enable PHP error reporting: In a development environment, add at the top of public/index.php or in Laravel’s config/app.php: ```php ini_set('display_errors', 1); error_reporting(E_ALL); ``` Framework logs: Laravel: tail -n 50 storage/logs/laravel.log Symfony: tail -n 50 var/log/prod.log Disable recently installed plugins: If you installed a new plugin or theme, deactivate it to see if the error resolves. Verify file permissions: Ensure correct ownership and permissions: ```bash chown -R www-data:www-data /var/www/html find /var/www/html -type d -exec chmod 755 {} \; find /var/www/html -type f -exec chmod 644 {} \; ```