You should first run update, then upgrade. Neither of them automatically runs the other.
apt-get update updates the list of available packages and their versions, but it does not install or upgrade any packages.apt-get upgrade actually installs newer versions of the packages you have. After updating the lists, the package manager knows about available updates for the software you have installed. This is why you first want to update.说白了就是一个更新包的版本 列表 并不安装 一个 安装
apt-get updete以及apt-get upgrade的区别,布布扣,bubuko.com
apt-get updete以及apt-get upgrade的区别
原文：http://www.cnblogs.com/Goden/p/3915642.html