在我的 15.04 ubuntu（我把它作为虚拟服务器）上，我想安装 unity ......但是一步一步地拳头软件属性，但我得到了：
sudo apt-get install software-properties-common
Reading package lists... Done
Building dependency tree... Done
E: Unable to locate package software-properties-common
有人可以帮助如何继续吗？
/# cat /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu vivid main restricted universe
deb http://archive.ubuntu.com/ubuntu vivid-updates main restricted universe
deb http://security.ubuntu.com/ubuntu vivid-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu vivid partner
/# sudo apt-get update
Get:1 http://security.ubuntu.com vivid-security InRelease [64.4 kB]
Get:2 http://archive.ubuntu.com vivid InRelease [218 kB]
Get:3 http://archive.canonical.com vivid InRelease [10.3 kB]
Get:4 http://archive.canonical.com vivid/partner amd64 Packages [2978 B]
Get:5 …