nginx配置文件里server_name为_是什么意思？

Question

还有这个配置文件不是很明白，能不能解释下，注释掉的就不管，##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# http://wiki.nginx.org/Pitfalls
# http://wiki.nginx.org/QuickStart
# http://wiki.nginx.org/Configuration
#
# Generally, you will want to move this file somewhere, and start with a clean
# file but keep this around for reference. Or just disable in sites-enabled.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##

# Default server configuration
#
server {
    listen 80 default_server;//这个是默认监听端口号 80 可是谁监听谁，nginx监听电脑上的80端口么
    listen [::]:80 default_server;

    # SSL configuration  
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;  //这个好像是我如果写一个静态网页可以在这个路径下写然后在环回地址显示，，具体是什么不明白求解释

    # Add index.php to the list if you are using PHP
    index index.html index.htm index.nginx-debian.html;//不明白 就是一堆html文件

    server_name _;//也不明白  别人说配的域名

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }//普通定位 但是也不明白

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
    
        # With php7.0-cgi alone:
        #fastcgi_pass 127.0.0.1:9000;
        # With php7.0-fpm:
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
    } //正则匹配如果后缀是php网页就进行php解析么，

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #    deny all;
    #}
}


# Virtual Host configuration for example.com
#
# You can move that to a different file under sites-available/ and symlink that
# to sites-enabled/ to enable it.
#
#server {
#    listen 80;
#    listen [::]:80;
#
#    server_name example.com;
#
#    root /var/www/example.com;
#    index index.html;
#
#    location / {
#        try_files $uri $uri/ =404;
#    }
#}
//最好能把这个文件执行流程说一遍，我找了很多资料都是零零散散的

Answer 1

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Answer 2

在所有服务器示例中，可以看到一个奇怪的名称“ _”：它只是无数的无效域名之一，同样可以使用其他无效名称，例如“-”和“！@＃”。

Answer 3

servername，配置域名的，必须是已经映射的域名，index 后边的 是可执行的文件后缀，。php  。htm 。html都行，include 引用其他配置文件。