Custom 404 page not displaying - nginx

Question

I just started with Nginx, and did the basic configuration, regarding configuring the PHP FPM, and I've changed the index file to be index.php instead of index.html. I also managed to get a handle on URL rewriting, although omitted from my example below for simplicity.
But in the default configuration file, there is a section dedicated to error pages, which looks as if it's ready to "plug and play". I have uncommented them, but they don't work correctly. I've gone through some 404-related questions on Stackoverflow, everyone seems to recommend that as the correct syntax.
Maybe the order of instructions is wrong, however, this is from the original sample configuration, so I don't know why it wouldn't be working.
I have remove all the commented lines from the configuration file, what's left is this:
server {
listen 80 default_server;
listen [::]:80 default_server ipv6only=on;
root /var/www/html;
index index.php;
server_name localhost;
location / {
try_files $uri $uri/ index.php;
}
error_page 404 /404.html;
error_page 500 502 503 504 /50x.html;
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
include fastcgi_params;
}
}
Now, when I go to http://localhost/this-page-doesnt-exist, the browser displays a literal File not found., instead of the contents of my /404.html file.
Also, the permissions of my 404.html file is the same as the permissions for the index.php, which is 644. The owner is the same as well.
What could be wrong?

Answer 1

try_files is passing your request for a none-existent file to index.php. This is in turn sends the request to php-fpm. By default Nginx returns the response from php-fpm to the client which is what you are seeing.
Update your php-fpm config to look like this and inform Nginx to handle error codes in the response.
location ~ \.php$ {
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_intercept_errors on;
include fastcgi_params;
}
The documentation is here: fastcgi_intercept_errors