Linux distribution

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A Linux distribution Template:Fn is a Unix-like operating system comprising the Linux kernel and other assorted free software/open-source software, and possibly proprietary software.

Commercially backed distributions such as Red Hat, Ubuntu (backed by Canonical Ltd), SUSE (backed by Novell) and Mandriva, and community projects such as Debian and Gentoo assemble and test the software before releasing their distribution. There are currently over three hundred Linux distribution projects in active development, revising and improving their respective distributions.

1 History
2 Composition
3 Choosing a Linux distribution
4 Installation
- 4.1 Installation on an existing platform
- 4.2 Demonstration
5 Interdistribution issues
6 See also
7 Notes
8 External links

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History

Before the first Linux distributions, a would-be Linux user was required to be something of a Unix expert, not only knowing what libraries and executables were needed to successfully get the system to boot and run, but also important details concerning configuration and placement of files in the system.

Linux distributions began to appear soon after the Linux kernel was first used by individuals outside the original Linux programmers. They were more interested in developing the operating system than in application programs, the user interface, or convenient packaging.

Early distributions included:

MCC Interim Linux, which was made available to the public for download on the ftp server of University of Manchester in February, 1992;
TAMU, created by individuals at Texas A&M University about the same time, and
SLS (Softlanding Linux System).

None of these distributions were well-maintained, so Patrick Volkerding released a distribution based on SLS, which he called Slackware; this is the oldest distribution still in active development.

Linux distributions attracted users as an alternative to the DOS and Microsoft Windows operating systems on the PC, Mac OS on the Apple Macintosh and proprietary versions of Unix. Most early adopters were used to Unix from work or school. They embraced Linux for its stability, low (if any) cost, and for the inclusion of the source code for most or all of the software included.

The distributions were originally simply a convenience, but today they have become the usual resort even for Unix or Linux gurus. To date, Linux has proven more popular in the server market, primarily for Web and database servers (see also LAMP), than in the desktop market.

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Composition

A typical Linux distribution comprises a Linux kernel, GNU tools and libraries, additional software, documentation, a window system, window manager, and a desktop environment. Most of the included software is free software/open-source software which is distributed by its maintainers both as pre-compiled binaries and in source code form, allowing users to modify and compile the original source code if they wish. Other software included with some distributions may be proprietary and may not be available in source code form.

Many provide an installation system akin to that provided with other modern operating systems. Self-hosting distributions like Gentoo Linux and Linux From Scratch provide the source code of all software and include binaries only of a basic kernel, compilation tools, and an installer; the installer compiles all the software for the specific microarchitecture of the user's machine.

Distributions are normally segmented into packages, each package holding a specific application or service; examples of packages include a library for handling the PNG image format, a collection of fonts, or a web browser. The package is typically provided as compiled code with installation and removal of packages handled better than a simple file archiver. This software is said to be the package management system (PMS) of the distribution. Each package intended for such a PMS contains meta-information like description, version, "dependencies", etc. The package management system can evaluate this meta-information to allow package searches, to perform an automatic upgrade to a newer version, to check that all dependencies of a package are fulfilled and/or to fulfill them automatically. Package management systems include:

RPM — now RPM Package Manager, but originally Red Hat Package Manager, originally from Red Hat but now used by many other distributors as well
deb — Debian package, originally from Debian but also used by others like Knoppix and Ubuntu
tgz or tar.gz — standard tar + gzip, possibly with some extra control files — used by Slackware and others, or sometimes when distributing very simple handmade packages
ebuild — the file containing information on how to retrieve, compile, and install a package in Gentoo's Portage system using the command emerge. Typically these are source-primary installs, though binary packages can be installed in this fashion as well.
recipe — the file containing information on how to download, unpack, compile and install a package in Gobo Linux distribution using its Compile tool. This system is similar to the Gentoo's Portage, but is more simplistic in design.
src — building the packages from source (often binary packages are provided in parallel on many systems).
klik — klik aims to provide an easy way of getting software packages for most major distributions without the dependency problems so common in many other package formats.

Although Linux distributions typically contain much more software than proprietary operating systems, it is normal for local administrators to install software not included with the distribution. An example would be a newer version of a software application than that supplied with a distribution, or an alternative to that chosen by the distribution (e.g., KDE rather than GNOME or vice versa). If the additional software is distributed in source-only form, this approach requires local compilation. However, if additional software is locally added, the 'state' of the local system may fall out of synchronization with the state of the package manager's database. If so, the local administrator user will be required to take additional measures to ensure the entire system is kept up to date. The package manager may no longer be able to do so automatically.

Most distributions install packages, including the kernel and other core operating system components, in a predetermined configuration. Few now require or even permit configuration adjustments at first install time. This makes installation less daunting, particularly for new users, but is not always acceptable. For specific requirements, much software must be carefully configured to be useful, to work correctly with other software, or to be secure, and local administrators are often obliged to spend time reviewing and reconfiguring assorted software.

Some distributions go to considerable lengths to specifically adjust and customize most all the software included in the distribution. Not all do so. Some distributions provide configuration tools to assist in this process. Note that such adjustments are typically site-specific and it is not possible for anyone, including a distribution's designer, to pre-configure the software provided to meet individual requirements. As with all operating systems, Linux and its distributions impose a system administration obligation on its users/operators/owners. Linux distributors differ from most operating system vendors in not claiming that "no administration is required." This honesty can worry potential users who have been told otherwise in marketing claims of other operating systems.

By replacing everything provided in a distribution, an administrator may reach a 'distribution-less' state: everything was retrieved, compiled, configured, and installed locally. It is possible to build such a system from scratch, without using a distribution altogether. One needs a way to generate the first binaries until the system is self-hosting. This can be done via compilation on another system capable of building binaries for the intended target (possibly by cross-compilation). See for example Linux From Scratch.

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Choosing a Linux distribution

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The diversity of Linux distributions are composed of many technical, organizational, and philosophical variations. Technical variations include support for different hardware devices and systems or software package configurations. Organizational differences are often motivated by technical decisions but also by philosophical or even historical reasons.

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Installation

The most common method of installing Linux is by booting from a CD that contains the installation program and installable software. Such a CD can be burned from a downloaded ISO image, purchased alone for a low price, or can be obtained as part of a box set that may also include manuals and additional commercial software.

Some distributions such as Debian can be installed from a small set of floppy disks. After a basic system is installed, more software can be added by downloading it from the Internet or using CDs.

Still another mode of installation of Linux is to install on a powerful computer to use as a server and to use less powerful machines (perhaps without hard drives, with less memory and slower CPUs) as thin clients over the network. Clients can boot over the network from the server and display results and pass information to the server where all the applications run. The clients can be ordinary PCs with the addition of the network bootloader on a drive or network interface controller, and hard disk space and processor power can be offloaded onto the client machine if desired. The cost savings achieved by using thin clients can be invested in greater computing power or storage on the server.

Anaconda, one of the more popular installers, is used by Red Hat Linux, Fedora Core and other distributions to simplify the installation process.

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Installation on an existing platform

Some distributions let the user install Linux on top of their current system, such as WinLinux. Linux is installed to the Windows hard-disk partition, and can be started from inside Windows itself. Similar approaches include coLinux.

Virtual machines (such as Virtual PC or VMware) also enables Linux to be run inside another OS. The VM software simulates an isolated environment onto which the Linux system is installed. After everything is done, the virtual machine can be booted just as if it were an independent computer.

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Demonstration

The difficulty in quickly demonstrating Linux on the computer of a potential new user remains still an obstacle, slowing its adoption as a personal computing platform.

Distributions such as Knoppix can be run directly from a "live CD" running entirely in RAM, rather than installing it to the hard drive. Similarly, some minimal distributions such as tomsrtbt can be run directly from as little as 1 floppy disk without needing to change the hard drive contents.

Linux User Groups, or LUGs, still provide the primary face-to-face forum for demonstration of Linux. Commercial exhibitions provide Linux demonstrations to potential new users, especially corporate buyers.

The fastest approach is probably that of Workspot, which uses VNC to provide a free Linux desktop demo online.

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Interdistribution issues

The Free Standards Group is an organization formed by major software and hardware vendors that aims to improve interoperability between different distributions. Among their proposed standards are the Linux Standard Base, which defines a common ABI and packaging system for Linux, and the Filesystem Hierarchy Standard which recommends a standard filenaming chart, notably the basic directory names found on the root of the tree of any Linux filesystem. Those standards, however, see limited use, even among the distributions developed by members of the organization.

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Notes

Template:Fnb Linux distributions may also be referred to as GNU/Linux distributions, though the latter may more often refer to the Debian system. The term "distribution" often suffices and is at least sufficient enough to distinguish free operating systems like Linux/BSD from proprietary operating systems such as Microsoft Windows or Apple Mac OS X. The term "distribution" is often informally shortened to "distro."

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