【Debian管理员手册】第 5 章包管理系统：工具和基本原则

5.1. 二进制包的结构

5.2. 软件包元信息

5.2.1. 描述：control 文件
5.2.2. 配置脚本
5.2.3. 校验，配置文件列表

5.3. 源软件包的结构

5.3.1. 格式
5.3.2. Debian 中的使用

5.4. 通过dpkg来操作软件包

5.4.1. 安装软件包
5.4.2. 软件包移除
5.4.3. 查询 dpkg 的数据库，并检查 .deb 文件
5.4.4. dpkg的日志文件
5.4.5. 多架构支持

5.5. 与其它软件包共存

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。 This chapter describes the structure and contents of “binary” and “source” packages. The former are files directly usable by
dpkg, while the latter contain the source code, as well as instructions for building binary packages.

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
xz or sometimes
gzip 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 sidebar
工具
dpkg、
APT 和
ar). 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). If your system suffered some even more outrageous fortune, and even these don’t work (maybe the deepest system libraries are missing?), you should try the static version of
busybox (provided in the
busybox-static package), which is even more self-contained, and provides subcommands such as
busybox ar,
busybox tar and
busybox xz.
In case of a misfortune you better also have a backup of your system (see 第 9.10 节 “备份”).

工具dpkg、APT 和 ar

dpkg is the program that handles
.deb files (binary packages), notably extracting, analyzing, and unpacking them. APT (the abbreviation of “Advanced Packaging Tool”) is a group of programs that allows the execution of higher-level modifications to the system: installing or removing a package (while keeping dependencies satisfied), updating and upgrading the system, listing the available packages, etc. 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 archivefile 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.xz archive in the system’s root (
/):

# ar x dpkg_1.19.7_amd64.deb# tar -C / -p -xJf data.tar.xz

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 更详细地讨论手册页 (参见第 7.1.1 节 “手册页面”)。来看看
.deb 文件的内容：

$ ar t dpkg_1.19.7_amd64.debdebian-binary
control.tar.gz
data.tar.xz
$ ar x dpkg_1.19.7_amd64.deb$ lscontrol.tar.gz  data.tar.xz  debian-binary  dpkg_1.19.7_amd64.deb
$ tar tJf data.tar.xz | head -n 16./
./
./etc/
./etc/alternatives/
./etc/alternatives/README
./etc/cron.daily/
./etc/cron.daily/dpkg
./etc/dpkg/
./etc/dpkg/dpkg.cfg
./etc/dpkg/dpkg.cfg.d/
./etc/logrotate.d/
./etc/logrotate.d/alternatives
./etc/logrotate.d/dpkg
./sbin/
./sbin/start-stop-daemon
./usr/
./usr/bin/
$ tar tJf control.tar.xz./
./conffiles
./control
./md5sums
./postinst
./postrm
$ cat debian-binary2.0

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 package format version. In Debian
Buster it is still version 2.0.
control.tar.xz: This archive file contains all of the available meta-information, like the name and version of the package as well as some scripts to run before, during or after (un-)installation of it. Some of the 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, and if files shipped have been modified locally.
data.tar.xz, data.tar.bz2, data.tar.gz: This archive contains all of the files to be extracted from the package; this is where the executable files, libraries, documentation, etc., are all stored. Packages may use different compression formats, in which case the file will be named differently for
xz,
bzip2 or
gzip.