3.8 How to keep a mixed system
People are sometimes interested in using one of the Debian versions as its main system distribution and one or more packages from another branch.
To set up what is your main version of Debian you should edit the /etc/apt/apt.conf to contain the following line:
APT::Default-Release "version";
Where version is the version of Debian you want to use as the main distribution. The versions you can use are stable, testing and unstable. To install packages from another version, then, you must you APT in the following way:
# apt-get -t distribution install package
For that to work, though, you need at least one APT source line in your /etc/apt/sources.list for the distribution you want the package from, and the package must exist on that source.
You can also request a specific version of a package using the following sintax:
# apt-get install package=version
For example, the line below will install version 2.2.4-1 of the nautilus package.:
# apt-get install nautilus=2.2.4-1
IMPORTANT: the `unstable' version of Debian is the version to which the newest versions of Debian packages are uploaded first. This distribution sees all of the changes that packages go through, both small ones and more drastic ones which affect many packages or the whole system. For this reason, this version of the distribution should not be used by inexperienced users or by those who need proven stability.
The `testing' distribution is not necessarily best than `unstable', because it does not receive security updates quickly. For servers and other production systems stable should always be used.
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3.9 How to upgrade packages from specific versions of Debian
apt-show-versions provides a safe way for users of mixed distributions to upgrade their systems without getting more of the less-stable distribution than they had in mind. For instance, it is possible to upgrade just your unstable packages by running after having installed the apt-show-versions package:
# apt-get install `apt-show-versions -u -b | grep unstable`
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3.10 How to keep specific versions of packages installed (complex)
You may have occasion to modify something in a package and don't have time or don't want to port those changes to a new version of the program. Or, for instance, you may have just upgraded your Debian distribution to 3.0, but want to continue with the version of a certain package from Debian 2.2. You can "pin" the version you have installed so that it will not be upgraded.
Using this resource is simple. You just need to edit the file /etc/apt/preferences.
The format is simple:
Package: <package>
Pin: <pin definition>
Pin-Priority: <pin's priority>
For example, to keep package sylpheed that I have modified to use "reply-to-list" at version 0.4.99, I add:
Package: sylpheed
Pin: version 0.4.99*
Note that I used an * (asterisk). This is a "wildcard"; it say that I want that this "pin" to be valid for all versions beginning with 0.4.99. This is because Debian versions its packages with a "Debian revision" and I don't want to avoid the installation of these revisions. So, for instance, versions 0.4.99-1 and 0.4.99-10 will be installed as soon as they are made available. Note that if you modified the package you won't want to do things this way.
The Pin-Priority field is optional; if not specified, it defaults to 989.
Let's take a look at how pin priorities work. A priority lower than 0 indicates that the package should never be installed. Priorities 0 to 100 denote packages that are not installed and that have no available versions. These won't come into the version-choosing process. Priority 100 is the priority assigned to an installed package - for the installed version of a package to be replaced by a different version, the replacement must have a priority greater than 100.
Priorities above 100 indicate that a package should be installed. Typically, the installed version of a package is changed only to upgrade it to a newer version. Any priority between 100 and 1000 (inclusive) indicates this typical behavior. A package with such a priority will not downgrade to an available version with a lower version number. For instance, if I have sylpheed 0.5.3 installed and define a pin on sylpheed 0.4.99 with priority 999, package 0.4.99 will not be installed to satisfy the pin. To make a package "downgradable", to satisfy the pin, it needs possess a priority greater than 1000.
A pin can be specified on a package's version, release or origin.
Pinning on a version, as we have seen, supports literal version numbers as well as wildcards to specify several versions at one time.
Option release depends on the Release file from an APT repository or from a CD. This option may be of no use at all if you're using package repositories that don't provide this file. You may see the contents of the Release files that you have on /var/lib/apt/lists/. The parameters for a release are: a (archive), c (components), v (version), o (origin) and l (label).
An example:
Package: *
Pin: release v=2.2*,a=stable,c=main,o=Debian,l=Debian
Pin-Priority: 1001
In this example, we chose version 2.2* of Debian (which can be 2.2r2, 2.2r3 -- this accomodates "point releases" that typically include security fixes and other very important updates), the stable repository, section main (as opposed to contrib or non-free) and origin and label Debian. Origin (o=) defines who produced that Release file, the label (l=) defines the name of the distribution: Debian for Debian itself and Progeny for Progeny, for example. A sample Release file:
$ cat /var/lib/apt/lists/ftp.debian.org.br_debian_dists_potato_main_binary-i386_Release
Archive: stable
Version: 2.2r3
Component: main
Origin: Debian
Label: Debian
Architecture: i386
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Тема: upgrade na Debian ( Knoppix 3.3 ) (Прочетена 2393 пъти)
Jan 14, 2004, 02:14