PHP 7 DomDocument not found

Question

I try run command: app/console cache:clear

This return me error:

An error occurred when executing the \"\'cache:clear --no-warmup

Answer 1

just a minor addition to the answer. i'm using nginx with php version 7 and php-fpm. you must restart the php-fpm service in order for the updates to work, restarting nginx alone won't help