Nginx PHP-FPM display blank page for .PHP file on Ubuntu

Setting up new Nginx instance wasn't a funny thing as stated on most blogposts while it display blank page during startup. This is annoying when people set things up from scratches.

First thing first:

Check whether PHP-FPM is running:
$ ps -aux | grep php-fpm --color

$
$ ps -aux | grep php-fpm --color
root      1898  0.0  1.8 209928 18992 ?        Ss   11:48   0:00 php-fpm: master process (/etc/php/7.0/fpm/php-fpm.conf)                      
www-data  1900  0.0  0.6 210060  6660 ?        S    11:48   0:00 php-fpm: pool www                                                            
www-data  1901  0.0  0.5 210060  6088 ?        S    11:48   0:00 php-fpm: pool www   

Also, you may notice that running processes may be owned by someone else, like nginx, apache or whatsoever. Make sure user/group setting in php-fpm config file is referring to the same user/group as set in Nginx config file, like www-data/www-data.

Default location of php-fpm 7.0 config file:

/etc/php/7.0/fpm/pool.d/www.conf

Default location of Nginx config file:
/etc/nginx/sites-available/default

Back to the question about why nginx displays a balnk page instead? Let's take a look at the Nginx config file:

...
...
server {
        ...
        location ~ \.php$ {
                try_files $uri =404;
                fastcgi_split_path_info ^(.+\.php)(/.+)$;
                fastcgi_cache  microcache;
                fastcgi_cache_key $scheme$host$request_uri$request_method;
                fastcgi_cache_valid 200 301 302 30s;
                fastcgi_cache_use_stale updating error timeout invalid_header http_500;
                fastcgi_pass_header Set-Cookie;
                fastcgi_pass_header Cookie;
                fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
                fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
                fastcgi_index index.php;
                include fastcgi_params;
                # Fix for missing params and blank php page display problems
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                fastcgi_param PATH_TRANSLATED $document_root$fastcgi_script_name;

        }
}

The line "include fastcgi_params" actually refers to the file /etc/nginx/fastcgi_params which has various fastcgi_param variables initialized when calling. Unfortunately, two important variables went missing leading to an unknown blank page when startup.

They are SCRITP_FILENAME and PATH_TRANSLATED. Add them back to Nginx config file and PHP things execute again!

Ref: https://www.narga.net/avoid-nginx-wordpress-blank-page/