更新软件源:
1.首先备份源列表，而后用gedit或其他编辑器打开源列表文件：
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backupsudo gedit /etc/apt/sources.list
2.把找到的合适的源，替换掉sources.list中所有的内容，保存。
比如163的源为：（163的源列表地址：/.help/ubuntu.html）
deb /ubuntu/ karmic main restricted universe multiversedeb /ubuntu/ karmic-security main restricted universe multiversedeb /ubuntu/ karmic-updates main restricted universe multiversedeb /ubuntu/ karmic-proposed main restricted universe multiversedeb /ubuntu/ karmic-backports main restricted universe multiversedeb-src /ubuntu/ karmic main restricted universe multiversedeb-src /ubuntu/ karmic-security main restricted universe multiversedeb-src /ubuntu/ karmic-updates main restricted universe multiversedeb-src /ubuntu/ karmic-proposed main restricted universe multiversedeb-src /ubuntu/ karmic-backports main restricted universe multiverse
把上面的内容复制粘贴，替换掉sources.list的全部内容。
3.执行源的更新：
sudo apt-get update
4.然后，执行真正的软件更新：
sudo apt-get upgrade
