前言
Ubuntu9.04版本现在属于一个很老的版本了，它现在已经不被支持了，所以在安装包时提示出错。这是因为软件源已不可用，所以要换源。
1 ，先备份/etc/apt/sources.list文件。：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2 ，修改sources.list文件（即换源）
sudo gedit /etc/apt/sources.list
将以下内容复制到文件中:
deb http://old-releases.ubuntu.com/ubuntu/ jaunty main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ jaunty-security main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb http://old-releases.ubuntu.com/ubuntu/ jaunty-backports main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ jaunty main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ jaunty-security main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ jaunty-updates main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ jaunty-proposed main restricted universe multiverse
deb-src http://old-releases.ubuntu.com/ubuntu/ jaunty-backports main restricted universe multiverse
3 ，尝试更新
sudo apt-get update
更换源后，下载软件包应该不会有任何问题。