更换ubuntu源

1. 备份源列表 

sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup

2. 用gedit打开

sudo gedit /etc/apt/sources.list

3. 从下面列表中选择合适的源，替换掉文件中内容，保存编辑好的文件。

4. 刷新。 

sudo apt-get update                               更新源列表

sudo apt-get upgrade

注意：一定要执行刷新。

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中国科学技术大学更新服务器（教育网，推荐校园网和网通用户使用）：

deb intrepid main multiverse restricted universe

deb intrepid-backports main multiverse restricted universe

deb intrepid-proposed main multiverse restricted universe

deb intrepid-security main multiverse restricted universe

deb intrepid-updates main multiverse restricted universe

deb-src intrepid main multiverse restricted universe

deb-src intrepid-backports main multiverse restricted universe

deb-src intrepid-proposed main multiverse restricted universe

deb-src intrepid-security main multiverse restricted universe

deb-src intrepid-updates main multiverse restricted universe

mirror.rootguide.org更新服务器（上海市 电信）

deb intrepid main restricted universe multiverse

deb-src intrepid main restricted universe multiverse

deb intrepid-updates main restricted universe multiverse

deb-src intrepid-updates main restricted universe multiverse

deb intrepid-backports main restricted universe multiverse

deb-src intrepid-backports main restricted universe multiverse

deb intrepid-security main restricted universe multiverse

deb-src intrepid-security main restricted universe multiverse

deb intrepid-proposed main multiverse restricted universe

deb-src intrepid-proposed main restricted universe multiverse