安装服务器端的openssh

1. 安装 open ssh：

2. 辑配置文件，允许以 root 用户通过 ssh 登录：
   sudo vi /etc/ssh/sshd_config

找到：PermitRootLogin prohibit-password禁用

添加：PermitRootLogin yes

执行命令：sudo service ssh restart

安装openssh-server过程中，如若出现以下提示：

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package openssh-server is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

这个问题的原因是ubuntu的/etc/apt/source.list中的源比较旧了，需要更新一下，更新方法：

$ sudo apt-get -y update