how to setup subdomain on nginx ubuntu for file hosting

If your configuration looks like the one you posted:

server {
    listen 80; ## listen for ipv4; this line is default and implied
    #listen [::]:80 default ipv6only=on; ## listen for ipv6

    root /var/www/dl.domain.com/public_html;
    index index.html index.htm;

    # Make site accessible from http://localhost/
    188.27.10.28 dl.domain.com;
}

Then it’s not valid.

You can test your configuration with nginx -t. After I tested your server block, I get the following error:

$ nginx -t
2015/04/22 00:26:32 [emerg] 145#0: unknown directive "188.27.10.28" in /etc/nginx/nginx.conf:39
nginx: [emerg] unknown directive "188.27.10.28" in /etc/nginx/nginx.conf:39
nginx: configuration file /etc/nginx/nginx.conf test failed

This means that the line 188.27.10.28 dl.domain.com; is not valid. You can remove it or comment it out.

After this reload nginx with nginx reload and try it again.

I keep my fingers crossed that it works for you!

Try changing your listen and server_name directives to:

listen       80  default_server;
server_name  _;

This tells nginx to make your server block the default and respond if no other block matches the Host header. Earlier it would respond only to Host: example.com as defined in the tutorial.

Resource link.