What's the `_` meaning in nginx configuration?

Question

what's the _ meaning in nginx?

in a nginx.conf I see this config:

listen       8080;
server_name  _;

what's the _ meaning?

Answer 1

From the documentation:

There is nothing special about this name, it is just one of a myriad of invalid domain names which never intersect with any real name. Other invalid names like “--” and “!@#” may equally be used.

With current versions of Nginx, it is perfectly valid to remove the server_name directive from the server block, rather than specify it with a fake name.