更新debian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_backup
sudo 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debian源为：

deb http://mirrors.163.com/debian squeeze main non-free contrib  
deb http://mirrors.163.com/debian squeeze-proposed-updates main contrib non-free  
deb-src http://mirrors.163.com/debian squeeze main non-free contrib  
deb-src http://mirrors.163.com/debian squeeze-proposed-updates main contrib non-free  

  
deb http://mirrors.163.com/debian-security squeeze/updates main contrib non-free   
deb-src http://mirrors.163.com/debian-security squeeze/updates main contrib non-free   

 
deb http://http.us.debian.org/debian squeeze main contrib non-free  
deb http://non-us.debian.org/debian-non-US squeeze/non-US main contrib non-free  
deb http://security.debian.org squeeze/updates main contrib non-free  

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