你必须先设置Server的DNS名称:

You have to set the Server's DNS name first:

so perform the command
$ sudo gksu gedit  /etc/hostname  to edit the hostname file
add the line www.example.com

$ sudo  /etc/hosts and add the line:
127.0.0.1   www.example.com localhost

之后确保在创建或签署证书时使用该域名

After that make sure to use that domain name in creating or signing the certificate