无法访问localhost？

使用的是本机 ubuntu nginx做web服务器，奈何前段时间一直好好的，突然就无法连接localhost了，查了很多资料也无解。
nginx服务处于开启状态如下:

$ sudo service nginx status
 * nginx is running

/etc/nginx/nginx.conf是默认的没有动过, 其中的include也对，如下:

##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;

/etc/nginx/site-available中的default，如下:

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /usr/share/nginx/html;
    index index.html index.htm;

    server_name localhost;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
        # Uncomment to enable naxsi on this location
        # include /etc/nginx/naxsi.rules
    }

    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

        # With php5-cgi alone:
        fastcgi_pass 127.0.0.1:9000;
        # With php5-fpm:
        # kfastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one

}

然后访问localhost就如下:

请问是如何解决呢

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127.0.0.1也无法访问， 也没有开代理。

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解决了，但是不太理解;
我把site-available中的default文件 复制一份到/etc/nginx/conf.d/default.conf
然后

sudo nginx -t
sudo service nginx restart

就可以了。 不是说/etc/nginx/conf.d与/etc/nginx/site-available在他俩任何目录下写配置文件，都可以吗？

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$ cat /etc/hosts 

找一下 有没有 127.0.0.1 locahost
没有的话

# echo "127.0.0.1 locahost" >> /etc/hosts

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Nginx在ubuntu下的架构不同于centos或windows, 通常nginx的所有站点配置都放在/etc/nginx/site-availabl目录下， 但是请注意， 这只是可用的配置， 若你想开启莫条站点的配置比如(www.test.com), 你需要在/etc/nginx/site-enabled创建软连接

$ pwd
/etc/nginx/site-enabled

$ sudo ln -s /etc/nginx/site-availabl/www.test.com www.test.com

软连接创建好后， 重庆NG，

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是不是防火墙设置问题呢？