Can I hide all server / os info?

You can stop it outputting the version of Nginx and OS by adding

server_tokens off;

to a http, server, or location context.

Or if you want to remove the Server header completely, you need to compile Nginx with the Headers More module in, as the header is hard coded in the Nginx source, and this module allows changing any http headers.

 more_clear_headers Server;

However, there are many hidden ways servers perform by accident via their implementation which may help identify the system. e.g. How it responds to a bad SSL request. I don’t see a practical way of preventing this.

Some of the things I might suggest:

• change error templates
• block all ports except the services needed