当尝试更新“unity”包（以及一些其他相关包，包括unity-2d和libunity-2d-private0）时，apt-get告诉我无法更新，因为所需的依赖项是libxi6 > 2:1.6.99.1，但实际安装的版本是2:1.6.0-0ubuntu2.1。
我运行了apt-cache policy libxi6，可以看到版本2:1.7.1.901-1ubuntu1~precise1在“更新”源中可用，但我安装的版本来自“安全”源。遗憾的是，我的安全源的优先级 (990) 高于我的更新源 (900)，因此 apt-get 似乎无法解决依赖性问题。
我无法在 Launchpad 上看到与此依赖项失败有关的任何问题，因为我预计 precise-updates 中的 unity 版本需要libxi6在 security 中可用的，或者 precise-security 中会有一个具有正确依赖项的 unity 包。
/etc/apt/preferences.d/* 的内容:
Package: *
Pin: release a=precise-security
Pin-Priority: 990
Package: *
Pin: release a=precise-updates
Pin-Priority: 900
Package: *
Pin: release a=precise-proposed
Pin-Priority: 400
输出apt-cache policy：
100 /var/lib/dpkg/status
release a=now
500 https://private-ppa.launchpad.net/commercial-ppa-uploaders/steam/ubuntu/ precise/main i386 Packages
release v=12.04,o=LP-PPA-commercial-ppa-uploaders-steam,a=precise,n=precise,l=Steam,c=main
origin private-ppa.launchpad.net
500 https://private-ppa.launchpad.net/commercial-ppa-uploaders/steam/ubuntu/ precise/main amd64 Packages
release v=12.04,o=LP-PPA-commercial-ppa-uploaders-steam,a=precise,n=precise,l=Steam,c=main
origin private-ppa.launchpad.net
500 http://dl.google.com/linux/talkplugin/deb/ stable/main i386 Packages
release v=1.0,o=Google, Inc.,a=stable,n=stable,l=Google,c=main
origin dl.google.com
500 http://dl.google.com/linux/talkplugin/deb/ stable/main amd64 Packages
release v=1.0,o=Google, Inc.,a=stable,n=stable,l=Google,c=main
origin dl.google.com
500 http://repository.spotify.com/ stable/non-free i386 Packages
release c=non-free
origin repository.spotify.com
500 http://repository.spotify.com/ stable/non-free amd64 Packages
release c=non-free
origin repository.spotify.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/universe Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/universe Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/restricted Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/restricted Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/multiverse Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/multiverse Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/main Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/main Translation-en
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/universe i386 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/multiverse i386 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/main i386 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/restricted i386 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/universe amd64 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/multiverse amd64 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/main amd64 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
400 http://gb.archive.ubuntu.com/ubuntu/ precise-proposed/restricted amd64 Packages
release v=12.04,o=Ubuntu,a=precise-proposed,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
500 http://archive.canonical.com/ precise/partner i386 Packages
release v=12.04,o=Canonical,a=precise,n=precise,l=Partner archive,c=partner
origin archive.canonical.com
500 http://archive.canonical.com/ precise/partner amd64 Packages
release v=12.04,o=Canonical,a=precise,n=precise,l=Partner archive,c=partner
origin archive.canonical.com
500 http://extras.ubuntu.com/ubuntu/ precise/main i386 Packages
release v=12.04,o=LP-PPA-app-review-board,a=precise,n=precise,l=Application Review Board PPA,c=main
origin extras.ubuntu.com
500 http://extras.ubuntu.com/ubuntu/ precise/main amd64 Packages
release v=12.04,o=LP-PPA-app-review-board,a=precise,n=precise,l=Application Review Board PPA,c=main
origin extras.ubuntu.com
500 http://security.ubuntu.com/ubuntu/ precise-security/universe Translation-en
500 http://security.ubuntu.com/ubuntu/ precise-security/restricted Translation-en
500 http://security.ubuntu.com/ubuntu/ precise-security/multiverse Translation-en
500 http://security.ubuntu.com/ubuntu/ precise-security/main Translation-en
990 http://security.ubuntu.com/ubuntu/ precise-security/multiverse i386 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=multiverse
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/universe i386 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=universe
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/restricted i386 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=restricted
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/main i386 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=main
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/multiverse amd64 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=multiverse
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/universe amd64 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=universe
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/restricted amd64 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=restricted
origin security.ubuntu.com
990 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 Packages
release v=12.04,o=Ubuntu,a=precise-security,n=precise,l=Ubuntu,c=main
origin security.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/universe Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/restricted Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/multiverse Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/main Translation-en
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/multiverse i386 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/universe i386 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/restricted i386 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/main i386 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/multiverse amd64 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/universe amd64 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/restricted amd64 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
100 http://gb.archive.ubuntu.com/ubuntu/ precise-backports/main amd64 Packages
release v=12.04,o=Ubuntu,a=precise-backports,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/universe Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/universe Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/restricted Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/restricted Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/multiverse Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/multiverse Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main Translation-en
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/multiverse i386 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/universe i386 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/restricted i386 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main i386 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/multiverse amd64 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/universe amd64 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/restricted amd64 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
900 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
release v=12.04,o=Ubuntu,a=precise-updates,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/universe Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise/universe Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise/restricted Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise/restricted Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise/multiverse Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise/multiverse Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise/main Translation-en_GB
500 http://gb.archive.ubuntu.com/ubuntu/ precise/main Translation-en
500 http://gb.archive.ubuntu.com/ubuntu/ precise/multiverse i386 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/universe i386 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/restricted i386 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/main i386 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/multiverse amd64 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=multiverse
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=universe
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/restricted amd64 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=restricted
origin gb.archive.ubuntu.com
500 http://gb.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
release v=12.04,o=Ubuntu,a=precise,n=precise,l=Ubuntu,c=main
origin gb.archive.ubuntu.com
答案1
Package: *
Pin: release a=precise-security
Pin-Priority: 990
这里有一个问题。安全包总是有更高的版本字符串。总是。您无需设置软件包固定来优先选择这些软件包。除非任何用户偏好限制此行为（这就是您正在做的事情），否则 APT 将始终安装可用的更高版本。
我不知道你想用这些软件包固定功能实现什么目的，但它们会给你带来麻烦。软件包固定功能是为不同的软件包源（即 Ubuntu 和某种 PPA）设计的，通常用于操纵非官方源的优先级。建议的存储库始终具有较低的优先级，安全存储库始终每天自动升级。
我建议您降低 PPA 优先级（如果这是您想要控制的），而不是修改 Ubuntu 存储库。
如果你不想改变任何东西，你可以强制 apt 绑定到你的意愿，使用如下命令：
sudo apt-get install libxi6=2:1.7.1.901-1ubuntu1~precise1
或者
sudo apt-get install libxi6/precise-updates
但请记住，更新存储库始终会包含安全存储库所做的所有更改。