添加“skippy-xd”的 PPA 源后，仍然找不到该包：
majo@think:~$ sudo add-apt-repository ppa:landronimirc/skippy-xd
[sudo] password for majo:
You are about to add the following PPA to your system:
Fullscreen composited task-switcher for X11
Skippy-XD is a program that provides Exposé-like features found on the Mac
OS X operating system. It is a standalone application for providing a window
picker with live previews (including live video) on Linux desktops that run
an X server with compositing support. Thus it is not part of the window
manager, and the compositing is not being used all the time.
If you work with many windows, your desktop may begin to get cluttered. You
can use Skippy-XD to quickly and conveniently find the right window that you
are looking for. It allows you to press a hotkey and see miniature versions
of all your active windows at once.
To use Skippy-XD, you need Xfce (xfwm4) or a NetWM compliant window
manager (LXDE, Openbox-based window managers, etc.).
http://code.google.com/p/skippy-xd/
More info: https://launchpad.net/~landronimirc/+archive/skippy-xd
Press [ENTER] to continue or ctrl-c to cancel adding it
gpg: keyring `/tmp/tmp1q3041/secring.gpg' created
gpg: keyring `/tmp/tmp1q3041/pubring.gpg' created
gpg: requesting key 23A187B2 from hkp server keyserver.ubuntu.com
gpg: /tmp/tmp1q3041/trustdb.gpg: trustdb created
gpg: key 23A187B2: public key "Launchpad PPA for Landronimirc" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
OK
majo@think:~$ sudo apt-get update
...
Reading package lists... Done
majo@think:~$ sudo apt-get install skippy-xd
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package skippy-xd
majo@think:~$ apt-cache search skippy
majo@think:~$ apt-cache search skippy-xd
我在笔记本电脑上使用 ubuntu 13.04，并额外安装了 lubuntu-desktop。我的上网本也出现了同样的情况，我安装了干净的 lubuntu 13.04。不过，手动下载软件包并安装就可以了。所以这不是什么大问题。但我只是想知道为什么我无法让 PPA 正常工作。在此先感谢大家的任何建议。
答案1
最新编辑：简短回答是：skippy-xd缺少Build-Depends:对python软件包的依赖。这就是 PPA 自动构建失败并且存储库中没有软件包的原因。
根据PPA 页面今年 2 月，raring amd64 和 i386 的构建失败了。也许您想联系 PPA 所有者或自己构建软件包，看看是否可以修复它。您应该能够修复它，apt-get source skippy-xd因为apt-get build-dep skippy-xd源软件包可通过该 PPA 获得。
编辑：再检查一下，该 PPA 中没有 Raring 的二进制包。关于如何自行构建的快速提示：
$ sudo apt-get install build-essential
$ sudo apt-get build-dep skippy-xd
$ apt-get source skippy-xd
$ cd skippy-xd-0.5.1~hg20111223
$ dpkg-buildpackage -us -uc -rfakeroot
做好看到一些混乱的准备吧。毕竟它没有在 Launchpad 编译场上编译，而 PPA 所有者选择不关心它。
编辑2：
我刚刚在 Linux Mint 15 (基于 Ubuntu Raring) i386 上成功编译了它。检查构建日志在启动板上说：
dh build-arch
dh_testdir -a
dh_auto_configure -a
dh_auto_build -a
make[1]: Entering directory `/build/buildd/skippy-xd-0.5.1~hg20111223'
python configure_environment_header.py
make[1]: python: Command not found
make[1]: *** [environment.h] Error 127
make[1]: Leaving directory `/build/buildd/skippy-xd-0.5.1~hg20111223'
dh_auto_build: make -j1 returned exit code 2
make: *** [build-arch] Error 2
dpkg-buildpackage: error: debian/rules build-arch gave error exit status 2
******************************************************************************
Build finished at 20130207-2027
FAILED [dpkg-buildpackage died]
******************************************************************************
我觉得Build-Dep缺少了一个强制命令，当Build-Dep开发人员的机器（python）上有相关内容时，这是一个常见错误。这就是存在构建服务器的原因之一。遗憾的是，PPA 所有者没有检查构建结果。
最新编辑后的结论：
自行构建并使用您最喜欢的文件浏览器双击安装包。创建错误单或联系 PPA 所有者以解决此问题。
玩得开心！！
答案2
不要使用ppa:landronimirc/skippy-xd；即使所有构建都已修复，它也已经过时了。
改用ppa:landronimirc/skippy-xd-daily，提供最新的每日构建开发代码的Skippy-XD。所有构建都应按预期可用。