利用 certbot 申请 SSL 证书

1. 运行 sudo certbot --manual --preferred-challenges dns certonly
2. 会弹出提示

   Saving debug log to /var/log/letsencrypt/letsencrypt.log
   Plugins selected: Authenticator manual, Installer None
   Please enter in your domain name(s) (comma and/or space separated)  (Enter 'c'

   大致是让你输入要申请整数的域名，ctrl + c 取消输入

3. 当输入完域名之后，会提示

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   NOTE: The IP of this machine will be publicly logged as having requested this
   certificate. If you're running certbot in manual mode on a machine that is not
   your server, please ensure you're okay with that.
   
   Are you OK with your IP being logged?
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   (Y)es/(N)o: 

   大致是说，你的这台服务器的 ip 会被记录用来申请了这个域名的证书

   我们输入 y 来确认

4. 我们确认完之后，certbot 会提示

   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Please deploy a DNS TXT record under the name
   _acme-challenge.你要申请证书的域名 with the following value:
   
   随机字符串
   
   Before continuing, verify the record is deployed.
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Press Enter to Continue

   我们这个时候就需要到 DNS解析 里面添加一条 txt记录

   主机名为: _acme-challenge.你要申请证书的

   记录值为: 随机生成的字符串

5. 添加完毕之后等待半分钟到一分钟左右，以让 DNS 广播
6. 回到 ssh窗口 键入回车以确认
7. 稍等片刻 certbot 会提示申请成功，并且给出证书的详细信息。