第 5 章包管理系统：工具和基本原则

作为 Debian 系统管理员，你经常地要处理 .deb 包，因为它们包含一致的功能单元（应用程序、文档等），使得安装和维护更容易。所以了解它们是什么及如何使用它们是个好主意。

本章介绍了“二进制”和“源码”包的结构和内容。前者是 .deb 文件，可以用 dpkg 命令直接处理；而后者则包含程序的源代码，以及创建二进制包的说明。

5.1. 二进制包的结构

The Debian package format is designed so that its content may be extracted on any Unix system that has the classic commands ar, tar, and gzip (sometimes xz or bzip2). This seemingly trivial property is important for portability and disaster recovery.

Imagine, for example, that you mistakenly deleted the dpkg program, and that you could thus no longer install Debian packages. dpkg being a Debian package itself, it would seem your system would be done for... Fortunately, you know the format of a package and can therefore download the .deb file of the dpkg package and install it manually (see the “TOOLS” sidebar). If by some misfortune one or more of the programs ar, tar or gzip/xz/bzip2 have disappeared, you will only need to copy the missing program from another system (since each of these operates in a completely autonomous manner, without dependencies, a simple copy will suffice).

工具 dpkg、APT 和 ar

dpkg 是处理 .deb 文件的命令，尤其是解压、分析和解包它们。

APT 是一组允许对系统进行高级的修改的程序：安装或者删除一个软件包（并且保持依赖关系满足），更新系统，列出可用的软件包等。

As for the ar program, it allows handling files of the same name: ar t archive displays the list of files contained in such an archive, ar x archive extracts the files from the archive into the current working directory, ar d archive file deletes a file from the archive, etc. Its man page (ar(1)) documents all its other features. ar is a very rudimentary tool that a Unix administrator would only use on rare occasions, but admins routinely use tar, a more evolved archive and file management program. This is why it is easy to restore dpkg in the event of an erroneous deletion. You would only have to download the Debian package and extract the content from the data.tar.gz archive in the system's root (/):

# ar x dpkg_1.16.10_amd64.deb
# tar -C / -p -xzf data.tar.gz

基础知识 Man 手册注记

初学者可能会在看到“ar(1)”这样的文字注记时感到疑惑。这通常是个简写，它表示指向 man 手册第一类中标题是 ar 的页面。

有时这种注记也用来避免歧义，比如要区分清楚是 printf 命令，可以用 printf(1) 来指明，如果是 C 语言里的 printf 函数，就可以用 printf(3) 来引用。

第 7 章 问题的解决与相关信息的检索 discusses manual pages in further detail (see 第 7.1.1 节 “手册页面”).

来看看 .deb 文件的内容：

$ ar t dpkg_1.16.10_amd64.deb
debian-binary
control.tar.gz
data.tar.gz
$ ar x dpkg_1.16.10_i386.deb
$ ls
control.tar.gz  data.tar.gz  debian-binary  dpkg_1.16.10_i386.deb
$ tar tzf data.tar.gz | head -n 15
./
./var/
./var/lib/
./var/lib/dpkg/
./var/lib/dpkg/updates/
./var/lib/dpkg/alternatives/
./var/lib/dpkg/info/
./var/lib/dpkg/parts/
./usr/
./usr/share/
./usr/share/locale/
./usr/share/locale/sv/
./usr/share/locale/sv/LC_MESSAGES/
./usr/share/locale/sv/LC_MESSAGES/dpkg.mo
./usr/share/locale/it/
$ tar tzf control.tar.gz
./
./conffiles
./preinst
./md5sums
./control
./postrm
./prerm
./postinst
$ cat debian-binary
2.0

如你所见， Debian 包的 ar 存档格式由三个文件组成：

debian-binary. This is a text file which simply indicates the version of the .deb file used (in 2013: version 2.0).
control.tar.gz. This archive file contains all of the available meta-information, like the name and version of the package. Some of this meta-information allows package management tools to determine if it is possible to install or uninstall it, for example according to the list of packages already on the machine.
data.tar.gz，这个存档文件包含所有要被从软件包里解压缩出来的文件；这是可执行文件、文档等存储的地方。有些软件包可能会使用其它压缩格式，那样的话文件名会有所不同（bzip2 是 data.tar.bz2，XZ 是 data.tar.xz for XZ，LZMA 是 data.tar.lzma）。

第 5 章 包管理系统：工具和基本原则

5.1. 二进制包的结构

第 5 章包管理系统：工具和基本原则