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

今天晚上，在使用虛擬機安裝好UBUNTU
後，啓動終端，輸入sudo apt-get install vim

卻出現下面到錯誤，

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

根據字面的意思是源的問題。所以在終端裏輸入

sudo apt-get update

然後繼續 sudo apt-get install vim

就能正常安裝vim了。