Package vim is not available, but is referred to by another package.

今天晚上，在使用虚拟机安装好UBUNTU
后，启动终端，输入sudo apt-get install vim

却出现下面到错误，

Package vim 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

根据字面的意思是源的问题。所以在终端里输入

sudo apt-get update

然后继续 sudo apt-get install vim

就能正常安装vim了。