If you are running SimpleRisk on a RedHat-based Linux distribution and see an error saying something like:
PHP Fatal error: Class 'PDO' not found in /var/www/html/simplerisk/index.php on line 279
This is likely because the PHP PDO functions are not compiled into PHP by default in this distro and need to be added with the command:
yum install php-pdo
Once php-pdo has been installed you will need to restart Apache and it should work.