根域名做301跳转的方法：

1.在域名服务商，将根域名解析到目标服务器ip地址。

2.在nginx新建xxx.com.conf的vhost文件，内容如下：

vi xxx.com.conf
server {
listen 80;
server_name xxx.com;
rewrite ^(.*)$ http://www.xxx.com$1 permanent;
}
server {
listen 443 ssl http2;
server_name xxx.com;
rewrite ^(.*)$ https://www.xxx.com$1 permanent;
ssl_certificate certs/Nginx/1_www.xxx.com_bundle.crt;
ssl_certificate_key certs/Nginx/2_www.xxx.com.key;#由于这两个命令的默认值已经好几次发生了改变，因此不建议显性定义，除非有需要额外定义的值
# ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
# ssl_ciphers HIGH:!aNULL:!MD5;
ssl_prefer_server_ciphers on;
charset utf-8;
access_log logs/localhost.access.log main;
error_log logs/localhost.error.log warn;
root html;
index index.php index.html index.htm;
location / {
……
}
}

3.这样在浏览器访问xxx.com，就会自动跳转到www.xxx.com了。