I did the command
chmod -R www-data:www-data /
But after that, nothing worked. So i found on the internet that you can returen back to your default permissions with:
perl -0ne '$_ =~ m{^(\d*\d\d\d) (.*)\0$} ; print "chmod $1 $2\n" ; chmod oct($1), $2 ;' working-permissions.txt
But is there some that could work with the groupowners?