Poglavlje 5. Sustav pakiranja: Alati i osnovni principi

Kao Debian administrator, morati cete rutinski baratati sa .deb paketima, obzirom da oni sadrže konzistentne funkcinalne jedinice (aplikacije, dokumentaciju, itd.), čiju instalaciju i održavanje olakšavaju. Stoga je dobra ideja znati što su oni i kako ih upotrebljavati.

Ovo poglavlje opisuje strukturu i sadržaj "binarnog" i "izvornog" paketa. Binarne su .deb datoteke direktno primijenjive koristeći dpkg, dok izvorni dio sadrži izvorni kod, kao i instrukcije za kreiranje binarnog paketa.

5.1. Struktura Binarnog paketa

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 (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 ALATI dpkg, APT i 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.

ALATI dpkg, APT i ar

dpkg je naredba koja manipulira sa .deb datotekama, pogotovo njihovim raspakiravanjem, analiziranjem te ekstrakcijom.

APT je grupa programa koji onogućuju izvršavanje modifikacija sustava na višoj razini: instalanje ili uklanjanje paketa (pri tome zadovoljavajući sve međusobne poveznice), nadogradnja sustava, pregled ponuđenih paketa, itd.

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.xz archive in the system's root (/):

# ar x dpkg_1.18.24_amd64.deb
# tar -C / -p -xJf data.tar.xz

POVRATAK OSNOVAMA Notacija stranca pomoći

Za početnike je možda zbunjujuće kako pronaći referencu za “ar(1)” u literaturi. U biti to je referenca za stranice pomoći naslovljene ar u sekciji 1.

Ponekad je takva notacija upotrebljena da se uklone nedoumice, na primjer prilikom razlikovanja između printf naredbe koja isto može biti indicirana sa printf(1) te sa printf funkcijom u C programskom jeziku, koji je isto može biti referiran kao printf(3).

Poglavlje 7, Solving Problems and Finding Relevant Information daje više informacija o stranicama pomoći (pogledaj Odjeljak 7.1.1, “Manual Pages”).

Pogledajte u sadržaj .deb datoteke:

$ ar t dpkg_1.18.24_amd64.deb
debian-binary
control.tar.gz
data.tar.xz
$ ar x dpkg_1.18.24_amd64.deb
$ ls
control.tar.gz  data.tar.xz  debian-binary  dpkg_1.18.24_amd64.deb
$ tar tJf data.tar.xz | head -n 15
./
./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/dpkg
./sbin/
./sbin/start-stop-daemon
./usr/
./usr/bin/
$ tar tzf control.tar.gz
./
./conffiles
./postinst
./md5sums
./prerm
./control
./postrm
$ cat debian-binary
2.0

Kao što vidite, ar arhiva Debian paketa je sačinjena od tri datoteke:

debian-binary. This is a text file which simply indicates the version of the .deb file used (in 2017: version 2.0).
control.tar.gz. Ova arhiva sadrži sve dostupne meta-informacije, kao šta su ime i verzija paketa. Neke od tih meta-informacija im omogućuju procjenu da li se paket može ili ne može instalirati, kao i ukloniti, a sve to u sukladnosti sa listom postojećih paketa u sustavu.
data.tar.xz. This archive contains all of the files to be extracted from the package; this is where the executable files, documentation, etc., are all stored. Some packages may use other compression formats, in which case the file will be named differently (data.tar.bz2 for bzip2, data.tar.gz for gzip).