Ubuntu下载vim

在sudo -s进入root模式，然后使用apt-get install vim进行vim的下载
但是出现错误

 Reading package lists... Done  
    Building dependency tree         
    Reading state information... Done  
    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  
    E: Package vim has no installation candidate 

解决方法：首先使用这个命令
apt-get update && apt-get install vim
然后再使用命令apt-get install vim
就可以完成