Examine owner and permissions of paths
The ownership of an entire path hierarchy is important when nginx needs to
read static content. For instance, the path
/var/www/site.com/one/two/three/numbers.html may be problematic when
directory three is owned by root rather than www-data. Nginx will
respond with status code 403 (forbidden) when http://site.com/one/two/three/numbers.html is accessed.
To debug this scenario we need to examine the owners and pemissions of each of the directories that lead to numbers.html. This can be accomplished in linux with the handy namei command in combination with realpath.
Real path will return the fullpath for the file.
> realpath numbers.html
/var/www/site.com/one/two/three/numbers.html
And namei -l <full_path> will examine each step in the file's directory structure.
> namei -l $(realpath numbers.html)
drwxr-xr-x root root /
drwxr-xr-x root root var
drwxr-xr-x www-data www-data www
drwxr-xr-x www-data www-data site.com
drwxr-xr-x www-data www-data one
drwxr-xr-x root root two
drwxr-xr-x www-data www-data three
-rw-r--r-- www-data www-data numbers.html
Ah there it is. The directory two is owned by root rather that www-data. chown will help you from here.