nginx server_name wildcard or catch-all

As a convention, the underscore is used as a server name for default servers.

From http://nginx.org/en/docs/http/server_names.html

In catch-all server examples the strange name “_” can be seen:

server {
   listen       80  default_server;
   server_name  _;
   return       444;
}

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.

Note that server_name _; alone is not enough. The above example only works because of default_server in the listen directive.

Change listen option to this in your catch-all server block. (Add default_server) this will take all your non-defined connections (on the specified port).

listen       80  default_server;

if you want to push everything to index.php if the file or folder does not exist;

try_files                       $uri /$uri /index.php;

Per the docs, It can also be set explicitly which server should be default, with the **default_server** parameter in the listen directive