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Capítulo 5. Sistema de paquetes: herramientas y principios fundamentales

5.1. Estructura de un paquete binario
5.2. Metainformación de un paquete
5.2.1. Descripción: el archivo control
5.2.2. Scripts de configuración
5.2.3. Sumas de verificación («checksum»), lista de archivos de configuración
5.3. Estructura de un paquete fuente
5.3.1. Formato
5.3.2. Utilización dentro de Debian
5.4. Manipulación de paquetes con dpkg
5.4.1. Instalación de paquetes
5.4.2. Eliminación de un paquete
5.4.3. Consulta de la base de datos de dpkg e inspección de archivos .deb
5.4.4. Archivo de registro de dpkg
5.4.5. Compatibilidad multiarquitectura
5.5. Coexistencia con otros sistemas de paquetes
Como un administrador de un sistema Debian generalmente manejará paquetes .deb ya que contienen unidades funcionales consistentes (aplicaciones, documentación, etc.) facilitando su instalación y mantenimiento. Por lo tanto, es buena idea saber qué son y cómo utilizarlos.
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. Estructura de un paquete binario

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 HERRAMIENTAS dpkg, APT y 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 Sección 9.10, “Respaldo”).
Estos son los contenidos de un archivo .deb:
$ 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
Como puede ver, el compendio ar de un paquete Debian contiene tres archivos:
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.