未捕获的异常'PDOException',消息'找不到驱动程序'

大家好我需要你的帮助

我收到了错误

Fatal error: Uncaught exception 'PDOException' with message 'could not find driver' in /home/rails/public_html/newidenty/server.php:12 Stack trace: 
#0 /home/rails/public_html/newidenty/server.php(12): PDO->__construct('mysql:dbname=ra...', 'rails_identy', 'rails_identy') 
#1 /home/rails/public_html/newidenty/registration.php(2): include('/home/rails/pub...') 
#2 {main} thrown in /home/rails/public_html/newidenty/server.php on line 12.

我正在使用118.139.182.107/~rails/HTML/test.php拥有PHP版本的所有信息并显示PDO库.

我的主机提供说他们在其中安装PDO但是遇到问题

我的代码是

 $dsn, 'username' => $username, 'password' => $password));

    // Pass a storage object or array of storage objects to the OAuth2 server class
    $server = new OAuth2\Server($storage);

    // Add the "Client Credentials" grant type (it is the simplest of the grant types)
    $server->addGrantType(new OAuth2\GrantType\ClientCredentials($storage));

    // Add the "Authorization Code" grant type (this is where the oauth magic happens)
    $server->addGrantType(new OAuth2\GrantType\AuthorizationCode($storage));

?>

请帮忙..