1.The authenticity of host ‘localhost (::1)’ can’t be established.

方法1

ssh -o StrictHostKeyChecking=no 192.168.121.xxx

方法2

修改/etc/ssh/ssh_config文件（或$HOME/.ssh/config）中的配置，添加如下两行配置：

StrictHostKeyChecking no
UserKnownHostsFile /dev/null

修改好配置后，重新启动sshd服务即可。

service sshd restart
#或者
systemctl restart sshd.service

2 取消/var/spool/mail/root邮件提醒

[root@slaver1 ~] vi /etc/profile
#添加如下内容
unset MAILCHECK
[root@slaver1 ~] source /etc/profile