nginx wrong with systemd (no replies)

default.conf
location / {
#root /usr/share/nginx/html;
root /sdd/;
#index index.html index.htm;
autoindex on;
[root@centos /]# /usr/sbin/nginx -c /etc/nginx/nginx.conf
I can read the files
[root@centos /]systemd start nginx
403 Forbidden
nginx/1.9.15
I add User=root to nginx.serivce
the question still have