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APT NASIL
Bölüm 2 - Introduction to the Debian archive


2.1 Introduction to Debian suites

Debian development happens in a model where we have three main "trees" which we call "suites": the stable suite is the last released version of Debian; the testing suite contains theoretically a always-ready-to-release version, packages come from the unstable branch after being there for 10 days with no critical problems reported and after being built on all release architectures; the unstable suite is where development happens: all new packages go to unstable to be tested for releasability and, then, end up in testing.

The stable suite never receives new versions of packages, just new revisions to fix security or critical problems. It is supposed to remain stable, meaning that the admin need not expect changes in configuration or behavior of the software they administer.

There is another suite which is treated differently from the usual ones by many tools: the experimental suite. First of all, it is not a self-contained suite, meaning you cannot have a system installed simply from it, you usually need to use it together with one of the ones mentioned earlier: most times the unstable one is chosen.

It's treated differently because it is indeed highly experimental in nature. Packages which maintainers think are broken or not really ready to go in unstable come to experimental for wider testing by fearless maintainers. Please do not use experimental if you're not actually willing to help in development, taking care of the burden it might bring to you yourself.


2.2 Debian sections

Each suite of a Debian repository is usually composed of one or more sections; their names and purposes may vary from one distributor to the other. Debian itself has three sections: main, contrib and non-free.

The main section is what Debian actually is, officially. All the software that conforms to the Debian Free Software Guidelines (DFSG) and only depends on DFSG-conformant software come to this section of the archive, complying with the Social Contract. Through these documents, and by promising to only allow software that complies with them to enter the main section, Debian provides a reasonably clear basic standard of freedom which users can rely on when installing software from main.

The contrib section is composed of DFSG-compliant software which depend on non-DFSG-compliant software or data to work. The non-free section is composed of software which do not conform to the DFSG but may be distributed. You should check the license of each software from non-free you want to install to evaluate if they're good enough for you to accept.


2.3 APT's chain of trust

APT comes equipped with a cryptographic chain-of-trust that extends from the debian developers to the end users.

The chain starts with the package maintainers who sign and upload their packages. Each signature is checked against the packager's key which was uploaded when they became an official Debian developer. This key was itself verified personally by other Debian developers.

Once the uploaded package is verified as having been signed by the maintainer, an MD5 sum of the package is computed and put in the Packages file. The MD5 sums of all of the Packages files are then computed and put into the Release file. The Release file is then signed by the archive key which is created once a year and distributed by the FTP server. This key is also on the Debian keyring.

Therefore, the end user, having added the archive key to his keyring , can check that the Release file was signed by the proper key, the MD5 sums of all the Packages files, and the MD5 sums of all the Debian packages. APT automates this process:

During update (see Paket listesini güncelleme, Kısım 4.2), APT checks the signature of the Release files by using its keyring (see Paket kurma, Kısım 3.2 for information on this) and the MD5 sums of the Packages files (which are recorded in the Release files).

During upgrade or installation of a package (see Paket güncelleme, Kısım 4.7 and Paket kurma, Kısım 4.4 respectively) APT checks the MD5 sums of the packages (which are stored in the Packages files).

If any of these steps fails, the user is warned, and the process halts.


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APT NASIL

2.0.2 - October 2006

Gustavo Noronha Silva kov@debian.org
Çeviri: Murat Demirten murat@debian.org