nginx 502 bad gateway after ubuntu server restart

I have a situation with an ubuntu server that is configured to run with nginx and fastcgi. The problem is that after a restart any request is giving 502 bad gateway in browser.

In error log the error looks like this:

 connect() to unix:/var/run/fastcgi.socket-4 failed (2: No such file or directory) while connecting to upstream

after I create the file manually (i do not know if this is correct) the error is changing to:

connect() to unix:/var/run/fastcgi.socket-4 failed (111: Connection refused) while connecting to upstream

nginx server has configuration settings for each website like this:

 location ~ \.php$ {
                        fastcgi_pass                    unix:/var/run/fastcgi.socket-4;
                        fastcgi_param   GATEWAY_INTERFACE       CGI/1.1;
                        fastcgi_param   SERVER_SOFTWARE         nginx;
                        fastcgi_param   QUERY_STRING            $query_string;
                        fastcgi_param   REQUEST_METHOD          $request_method;
                        fastcgi_param   CONTENT_TYPE            $content_type;
                        fastcgi_param   CONTENT_LENGTH          $content_length;
                        fastcgi_param   SCRIPT_FILENAME         /document_root/$fastcgi_scr
                        fastcgi_param   SCRIPT_NAME             $fastcgi_script_name;
                        fastcgi_param   REQUEST_URI             $request_uri;
                        fastcgi_param   DOCUMENT_URI            $document_uri;
                        fastcgi_param   DOCUMENT_ROOT           /document_root;
                        fastcgi_param   SERVER_PROTOCOL         $server_protocol;
                        fastcgi_param   REMOTE_ADDR             $remote_addr;
                        fastcgi_param   REMOTE_PORT             $remote_port;
                        fastcgi_param   SERVER_ADDR             $server_addr;
                        fastcgi_param   SERVER_PORT             $server_port;
                        fastcgi_param   SERVER_NAME             $server_name;
                        fastcgi_param   REDIRECT_STATUS         200;
                        fastcgi_index                   index.php;
                        fastcgi_intercept_errors        on;
                        }

Note that I am quite new to nginx, however I have experience and knowhow in apache and php.

The 502 bad gateway error means that the backend server (which is php in your case) is not functioning properly, and since it was related to a server restart, I guessed it would be related to it not starting on boot time.

Since I didn't know the service name, running sudo service --status-all lists all services on the system.

After finding the php service name which turned to be spawn-fcgi in your case, you can start it using