nginx和fastcgi的通信方式有两种

1、TCP: 
# 1、nginx
location ~ \.php$ {
      index index.php index.html index.htm;
      fastcgi_pass 127.0.0.1:9000;
      fastcgi_index index.php;
      include fastcgi_params;
 }


# 2、php-fpm
listen=127.0.0.1:9000
2、unix domain socket: 
# 1、新建fpm-cgi.sock
sudo touch /dev/shm/fpm-cgi.sock
sudo chown www-data:www-data /dev/shm/fpm-cgi.sock
sudo chmod 666 /dev/shm/fpm-cgi.sock


# 2、php-fpm
listen=/dev/shm/fpm-cgi.sock
listen.backlog = -1

# 3、nginx
location~\.php${
      index index.php index.html index.htm;
      include /etc/nginx/fastcgi_params;
      fastcgi_pass unix:/dev/shm/fpm-cgi.sock;
      fastcgi_index index.php;
      include fastcgi_params;
}

参考
nginx 和 php-fpm 通信使用unix socket还是TCP，及其配置