Description of problem:

There is a minor typo in the default server definition in /etc/nginx/nginx.conf

How reproducible:

# rpm -q nginx
nginx-1.10.2-1.el7.x86_64
# fgrep -A2 404.html /etc/nginx/nginx.conf
        error_page 404 /404.html;
            location = /40x.html {
        }
--
#        error_page 404 /404.html;
#            location = /40x.html {
#        }
# ls -1 /usr/share/nginx/html/*.html
/usr/share/nginx/html/404.html
/usr/share/nginx/html/50x.html
/usr/share/nginx/html/index.html
#

The intent of the "location = /40x.html" block was to inhibit any additional processing when a user hits a 404 error, however it seems that the line was copy-n-pasted from the 50x handler, was not properly updated, and become a no-op block in this configuration.

I think that the "location = /40x.html" lines should be fixed to be "location = /404.html" to achieve the desired effect.

P.S. The indentation in /etc/nginx/nginx.conf looks weird, e.g. these location definitions for error pages look weirdly indented.
P.P.S. Also the content of the error pages refers to Fedora while the package can be installed on RHEL and CentOS -- I'd suggest replace "Fedora" in the error page content with "EPEL" or something similar.