刚装好ubuntu9.04,一般默认的源很慢，所以要换源。
步骤一：备份文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
步骤二：编辑文件
sudo gedit /etc/apt/sources.list，清空原文件内容，以我的配置为例把下面的拷贝到文件中:
##Mirror.lupaworld.com更新服务器（浙江省杭州市双线服务器，推荐）
deb http://mirror.lupaworld.com/ubuntu intrepid main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu intrepid-security main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu intrepid-updates main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu intrepid-backports main restricted universe multiverse
deb http://mirror.lupaworld.com/ubuntu intrepid-proposed main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu intrepid main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu intrepid-security main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu intrepid-updates main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu intrepid-backports main restricted universe multiverse
deb-src http://mirror.lupaworld.com/ubuntu intrepid-proposed main restricted universe multiverse
##台湾的官方源速度也相当不错，有时甚至快于内地的
deb http://tw.archive.ubuntu.com/ubuntu jaunty main restricted universe multiverse
deb http://tw.archive.ubuntu.com/ubuntu jaunty-security main restricted universe multiverse
deb http://tw.archive.ubuntu.com/ubuntu jaunty-updates main restricted universe multiverse
deb http://tw.archive.ubuntu.com/ubuntu jaunty-backports main restricted universe multiverse
deb http://tw.archive.ubuntu.com/ubuntu jaunty-proposed main restricted universe multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu jaunty main restricted universe multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu jaunty-security main restricted universe multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu jaunty-updates main restricted universe multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu jaunty-backports main restricted universe multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu jaunty-proposed main restricted universe multiverse
##上海市上海交通大学更新服务器（教育网，推荐校园网和网通用户使用）
deb http://ftp.sjtu.edu.cn/ubuntu/ jaunty main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ jaunty-backports main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ jaunty-proposed main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ jaunty-security main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ jaunty-updates main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ jaunty main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ jaunty-backports main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ jaunty-proposed main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ jaunty-security main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ jaunty-updates main multiverse restricted universe
##网易163更新服务器
deb http://mirrors.163.com/ubuntu/ jaunty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jaunty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jaunty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jaunty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jaunty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jaunty-backports main restricted universe multiverse
##Archive.ubuntu.com更新服务器（欧洲，此为官方源，电信网通用户使用)
deb http://archive.ubuntu.com/ubuntu/ jaunty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ jaunty-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ jaunty-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ jaunty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ jaunty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ jaunty-backports main restricted universe multiverse
完后一定执行：
sudo apt-get update