我正在配置 Debian 6 (Squeeze) x86 服务器，并希望在需要时安装一些来自测试或不稳定的软件包，所以我使用固定。
我已将我的 /etc/apt/sources.list 配置如下：
deb http://ftp.br.debian.org/debian stable main
deb http://ftp.br.debian.org/debian stable-updates main
deb http://security.debian.org/ stable/updates main
deb http://backports.debian.org/debian-backports squeeze-backports main
deb http://ftp.br.debian.org/debian testing main
deb http://ftp.br.debian.org/debian testing-updates main
deb http://security.debian.org/ testing/updates main
deb http://ftp.br.debian.org/debian unstable main
我的 /etc/apt/preferences 如下：
Package: *
Pin: release a=stable
Pin-Priority: 700
Package: *
Pin: release a=stable-updates
Pin-Priority: 700
Package: *
Pin: release a=squeeze-backports
Pin-Priority: 675
Package: *
Pin: release a=testing
Pin-Priority: 650
Package: *
Pin: release a=testing-updates
Pin-Priority: 650
Package: …