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The core of an operating system is a piece of software that interacts with the hardware of the computer, and provides basic functionality for several applications. On Linux based systems, the so-called kernel provides this functionality, and the term Linux just means this core without those applications that provide the functionality for users. Other examples are the Hurd, or the flavours of the BSD kernel.
Many applications around UNIX-like kernels are provided by the GNU
system. That is why Linux based
operating systems are described as GNU/Linux systems. The GNU tools around the
Linux kernel build a complete operating system.
Users do not need only an operating system. They also need certain applications like web servers, or office suites. A distribution is a collection of software packages around the GNU/Linux operating system that satisfies the needs of the target user group. There are general distributions, which try to support all users, and there are several specialised distributions, which each target a special group of users.
Distributors are those companies that are building these collections of software around the GNU/Linux operating system. Because it is Free Software, the user who buys a distribution pays for the service that the distributor is providing. These services might be:
Preparing a useful collection of software around GNU/Linux.
Caring for smooth installation that the target user is able to manage.
Providing software updates and security fixes.
Writing documentation and translations to enable the user to use the distribution with maximum effect.
Selling Boxes with ready to install CDs and printed documentation.
Offering training and qualification.
Most distributors ship their distribution in binary packages. Two package formats are widely used:
which is supported by RedHat, SuSE, Mandrake and others.
used by Debian and derived distributions.
All GNU/Linux distributions have a certain amount of common ground, and the
Linux Standard Base
(LSB)
is attempting to develop and promote a set of standards that will increase
compatibility among Linux distributions, and enable software applications to
run on any compliant system.
The very essence of any distribution, (whether delivered as RPMs, DEBs, Source tarballs or ports) is the choice of policy statements made (or not made, as the case may be) by the creators of the distribution.
Policy statements in this sense are things like "configuration
files live in /etc/$package/$package.conf
, logfiles go to
/var/log/$package/$package.log
and the documentation files can be
found in /usr/share/doc/$package
."
The policy statements are followed by the tool-chains and libraries used to build the software, and the lists of dependencies, which dictate the prerequisites and order in which the software has to be built and installed. (It's easier to ride a bicycle if you put the wheels on first. ;-) )
It is this adherence to policy that causes a distribution to remain
consistent within its own bounds. At the same time, this is the reason why
packages can not always be safely installed across distribution boundaries. A
SuSE package.rpm
might not play well with a RedHat
package.rpm
, although the packages work perfectly well within
their own distributions. A similar compatability problem could also apply to
packages from the same distributor, but from a different version or generation
of the distribution.
As you will see later in more detail, Custom Debian Distributions are just a modified ruleset for producing a modified (specialised) version of Debian GNU/Linux.
A package management system is a very strong tool to manage software packages on your computer. A large amount of the work of a distributor is building these software packages.
Distributors you might know are Mandrake
, RedHat
, SuSE
(now owned by Novell
) and others.
Debian
is just one of them.
Well, at least this is what people who do not know Debian well might think about it. But, in fact, Debian is a different kind of distribution ...
The Debian Project is an association of individuals who have made common cause to create a free operating system. This operating system that we have created is called Debian GNU/Linux, or simply Debian for short.
Moreover, work is in progress to provide Debian of kernels other than Linux, primarily for the Hurd. Other possible kernels are the flavours of BSD, and there are even people who think about ports to MS Windows.
All members of the Debian project are connected in a web of
trust
, which is woven by signing GPG keys. One requirement to
become a member of the Debian project is to have a GPG key signed by a Debian
developer. Every time one Debian developer meets another developer for the
first time, they sign each other's keys. In this way, the web of trust is
woven.
Debian is not a company, but an organisation.
It does not sell anything.
Debian members are volunteers.
Maintainers are working on the common goal: to build the best operating system they can achieve.
Debian maintains the largest collection of ready-to-install Free Software on the Internet.
There are two ways to obtain Debian GNU/Linux:
Buy it from some other distributor on CD. Perhaps the correct term would be redistributor. Because Debian is free, anybody can build his own distribution based on it, sell CDs, and even add new features, such as printed documentation, more software, support for different installers and more.
Download Debian from the web for free.
The latter is the common way, and there are really great tools to do it this way. Certainly it is always possible to copy Debian from a friend.
Debian contains nearly 10000 binary packages, and this number is constantly increasing. There is no single user who needs all these packages (even if conflicting packages are not considered).
The normal user is interested in a subset of these packages. But how does the user find out which packages are really interesting?
One solution is provided by the tasksel
package. It provides a
reasonable selection of quite general tasks that can be accomplished using a
set of packages installed on a Debian GNU/Linux system. But this is not really
fine grained, and does not address all of the needs of user groups with special
interests.
Custom Debian Distributions (formerly known as Debian Internal Projects) try to provide a solution for special groups of target users with different skills and interests. Not only do they provide handy collections of specific program packages, but they also ease installation and configuration for the intended purpose.
To clarify a common misunderstanding: Custom Debian Distributions are not forks from Debian. They are completely included, and if you obtain the complete Debian GNU/Linux distribution, you have all available Custom Debian Distributions included.
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Custom Debian Distributions
4 April 2008tille@debian.org