Symfony - 如何设置从dev到prod？

I know that this is not the first post about this question, but I do it because others answers didn't solve my problem.

I tried the basic :

$kernel = new AppKernel('prod', true);

But this is not the good way to do it because I still have Symfony errors... I don't know how to rewrite errors pages :

http://le-blog-etudiant.fr/blablabla

Do you know if this Symfony error is caused by the fact that my website is still in dev mode or because my error.html.twig page doesn't work ?

EDIT 1 :

I'm using app.php on my site, I set $kernel = new AppKernel('prod', false); and I did the command : php bin/console cache:clear --env=prod but it still display Symfony's errors

Because you need to do this :

$kernel = new AppKernel('prod', false);

Here is the constructor of AppKernel :

/**
 * Constructor.
 *
 * @param string $environment The environment
 * @param bool   $debug       Whether to enable debugging or not
 */
public function __construct($environment, $debug)

Permission denied here showing your problem http://le-blog-etudiant.fr

You have to give permission

chmod 777 -R var/cache

chmod 777 -R var/cache/*