I can not add a comment to this post - https://stackoverflow.com/a/21797786/6143954.
So I created a new question.
It was the correct answer before it was edited. In this answer, the line
sudo chmod -R 770 /var/www/
is replaced by
sudo chmod -R 760 /var/www/
Specifically, this solution is not suitable for Django.
The answer should not be changed after it has been marked as the right solution.
That was the correct answer before correcting the original post.
The GOOD solution would be:
sudo groupadd varwwwusers
sudo adduser www-data varwwwusers
sudo chgrp -R varwwwusers /var/www/
sudo chmod -R 770 /var/www/
How correct is this solution?