首先要备份原来的源列表：
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
再用编辑器打开
sudo gedit /etc/apt/source.list
用下面的源替换掉文件中所有的内容，保存编辑好的文件:
deb http://ftp.xdlinux.info/ubuntu/ raring main multiverse restricted universe
deb http://ftp.xdlinux.info/ubuntu/ raring-backports main multiverse restricted universe
deb http://ftp.xdlinux.info/ubuntu/ raring-proposed main multiverse restricted universe
deb http://ftp.xdlinux.info/ubuntu/ raring-security main multiverse restricted universe
deb http://ftp.xdlinux.info/ubuntu/ raring-updates main multiverse restricted universe
deb-src http://ftp.xdlinux.info/ubuntu/ raring main multiverse restricted universe
deb-src http://ftp.xdlinux.info/ubuntu/ raring-backports main multiverse restricted universe
deb-src http://ftp.xdlinux.info/ubuntu/ raring-proposed main multiverse restricted universe
deb-src http://ftp.xdlinux.info/ubuntu/ raring-security main multiverse restricted universe
deb-src http://ftp.xdlinux.info/ubuntu/ raring-updates main multiverse restricted universe
注意上面的代号要换成相应版本的代号。例如，要换成ubuntu12.04的源，则只要将上面的raring换成precise。ubuntu主要版本的代号如下：
Ubuntu 10.04 - Lucid Lynx （清醒的猞猁）
Ubuntu 12.04 - Precise Pangolin （精准的穿山甲）
Ubuntu 12.10 - Quantal Quetzal （？）
Ubuntu 13.04 - Raring Ringtail
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