According to there documentation i needed to use phpinfo() to check for inconsistencies in my php.ini.
I have put it in the index.php because all other files are not accessable from the web. Or give error's like:
Fatal error: Uncaught Zend_Cache_Exception: cache_dir "/var/www/magento/var/page_cache" is not writable in /var/www/magento/vendor/magento/zendframework1/library/Zend/Cache.php:209
Is there a command like:
magento cache:opcache:reset ?