大赛试题内容：
5.所有Linux主机root用户使用完全合格域名免密码ssh登录到其他Linux主机。
解答过程：
在linux-1上设置
[root@host-10-10-70-101 ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.