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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 dpkgAPTar). 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”).
来看看 .deb 文件的内容:
$ ar t dpkg_1.19.7_amd64.deb
debian-binary
control.tar.gz
data.tar.xz
$ ar x dpkg_1.19.7_amd64.deb
$ ls
control.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-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 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.