Linux distribution

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A Linux distribution, often simply distribution or distro, is a member of the Linux family of Unix-like operating systems comprised of the Linux kernel, the non-kernel parts of the GNU operating system, and assorted other software. Linux distributions take a variety of forms, from fully-featured desktop and server operating systems to minimal environments (typically for use in embedded systems, or for booting from a floppy).

To provide a Unix-like environment, Linux distributions contain a set of Unix-like utilities and the libraries needed to support them. In full-featured distributions these are generally taken from the GNU operating system. Distributions optimized for size tend to use more compact alternatives like busybox and uclibc.

There are currently over three hundred Linux distribution projects in active development, constantly revising and improving their respective distributions. One can distinguish between commercially-backed distributions, such as Fedora Core (Red Hat), SUSE Linux (Novell), Ubuntu (Canonical Ltd.) and Mandriva Linux and community distributions such as Debian and Gentoo. Usually, the procedures for assembling and testing a distribution prior to release are more elaborate the bigger the user base for the distribution is.

1 History
2 Components
- 2.1 Package management
3 Choosing a Linux distribution
- 3.1 Demonstration
- 3.2 Interdistribution issues
4 Installation
- 4.1 Installation on an existing platform
- 4.2 Installation through an existing platform
5 Proprietary software
6 OEM Contracts
7 See also
8 Notes
9 External links

[edit] 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 they were in application programs, the user interface, or convenient packaging.

Early distributions included:

H J Lu's "Boot-root" a two disk pair with the kernel and the absolute minimal tools to get started.
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).

SLS was not well-maintained, so Patrick Volkerding released a distribution based on SLS, which he called Slackware; released July 16, 1993 ^[1]. This is the oldest distribution still in active development.

Users were attracted to Linux distributions as alternatives 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 familiar with Unix from work or school. They embraced Linux for its stability, low (if any) cost, and for the availability 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 choice even for Unix or Linux experts. 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.

[edit] Components

A typical desktop 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.

[edit] Package management

See also: Package management system and Linux package formats

Distributions are normally segmented into packages. Each package contains 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 by a package management system (PMS) rather than a simple file archiver. Each package intended for such a PMS contains meta-information such as a package description, version, and "dependencies". 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.

Although Linux distributions typically contain much more software than proprietary operating systems, it is normal for local administrators to install software not included in 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 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 or all of 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 require its users/operators/owners to perform system administration. 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, avoiding 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.

[edit] Choosing a Linux distribution

Further information: Comparison of Linux distributions and LiveDistro

Broadly, Linux distributions may be:

commercial or non-commercial;
designed for enterprise or for home usage;
designed for servers, desktops, or embedded devices;
targeted at regular users or power users;
general purpose or highly specialized toward specific machine functionalities, for example firewalls, network routers, and compute clusters;
designed and even certified for specific hardware and computer architectures;
targeted at specific user groups, for example through language internationalization and localization, or through inclusion of many music production or scientific computing packages.

The diversity of Linux distributions is due to technical, organizational, and philosophical variation amongst vendors and users. The permissive licensing of most GNU/Linux software means that any user with sufficient knowledge and interest can customize an existing distribution or design his or her own needs. Technical variations include support for different hardware devices and systems or software package configurations. Other differences are motivated either by technical decisions, philosophical or even historical reasons. Some distributions specialize in use on desktops, servers or routers. Other criteria include security (and how often security updates are available), ease of package management and the number of binary packages available.

There are tools available to help making the decision, such as several different versions of the Linux Distribution Chooser ^[2] ^[3] ^[4] and the universal package search tool, whohas.^[5] There are some easy ways to try out several Linux distributions before deciding on one. Multi Distro is a Live CD that contains nine space-saving distributions.^[6] Tools are available to make such CDs and DVDs, among them Nautopia.^[7] In fact, it is not necessary to burn a Live CD in the first place. Virtual machines such as QEMU and VMware permit booting of LiveCD image files. In the case of VMware, this requires a specific virtual machine to be downloaded.^[8] ^[9] In QEMU, the functionality is already included.

Details and interest rankings of Linux distributions are available on DistroWatch and a fairly comprehensive list of Live CDs is The LiveCD List. Some websites such as OSDir.com and OSVids.com offer screenshots and videos as a means to getting a first impression of various distributions. Each distro has its own merits and demerits, making selection of a distro a matter of matching needs and attitudes, with distro philosophy and software contents. One popular distro ranking site is DistroWatch. Nevertheless, well-known Linux distributions include:

Slackware, one of the first Linux distributions, founded in 1993, and since then actively maintained by Patrick J. Volkerding
Debian, a non-commercial distribution maintained by a volunteer developer community with a strong commitment to free software principles
Ubuntu, a newly popular desktop distribution maintained by Canonical that is derived from Debian
Red Hat, maintained by the American company of the same name, which also provides a community version in the form of Fedora Core
Mandriva, a Red Hat derivative popular in France and Brazil, today maintained by the French company of the same name
SuSE, originally derived from Slackware with the system management software borrowed from Red Hat, maintained by the company Novell
Gentoo, a distribution targeted at power users, known for its FreeBSD Ports-like automated system for compiling applications from source code
Knoppix, a LiveCD distribution that runs completely from removable media and without installation to a hard disk
Linspire, a commercial desktop distribution based on Debian, and once the defendant in the Microsoft vs. Lindows lawsuit over its former name.

That multiple Linux distributions peacefully coexist severely limits the possibility of anti-competitive lawsuits comparable to those filed in the United States v. Microsoft and European Union v. Microsoft trials; these lawsuits exposed the danger to a sole company that extends its monopoly through vendor lock-in by controlling not only an operating system installed on the vast majority of computers but also an important collection of software that runs under that operating system. One inconvenience of this system is that the definition of a Linux operating system is somewhat unclear. Linux may be seen as either an operating system unto itself, or a family of operating systems, one for each distribution. The important point is that most Linux software is compatible across all major distributions, even at the binary level, and that only distribution-specific software will not work with another distribution.

[edit] Demonstration

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

However, Knoppix has pioneered the ability to run directly from a "live CD" running entirely in RAM, rather than installing it to the hard drive. Other distributions have followed suit, and live versions are available for, for example, SUSE, Ubuntu, Mepis, and others. 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 used VNC to provide a free Linux desktop demo online.

[edit] 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.

[edit] Installation

There are many ways to install a Linux distribution:

The most common method of installing Linux is by booting from a CD-ROM or DVD 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, provided as a cover disk with a magazine, in some cases shipped for free by request, or obtained as part of a box set that may also include manuals and additional commercial software. New users tend to begin by partitioning a hard-drive in order to keep an existing operating system. The Linux distribution can then be installed on the new partition without affecting previously saved data.
Early Linux distributions were installed using sets of floppies but this has been abandoned by all major distributions. Nowadays most distributions offer CD and DVD sets with the vital packages on the first disc and less important packages on later ones. They usually also allow installation over a network after booting from either a set of floppies or a CD with only a small amount of data on it.
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.
In a Live CD setup, the computer boots the entire operating system from CD without first installing it on the computer's hard disk. Some distributions have a Live CD installer, where the computer boots the operating system from the disk, and then proceeds to install it onto the computer's hard disk, providing a seamless transition from the OS running from the CD to the OS running from the hard disk.
Mini CD images allow Linux to be installed from a disk with a small form factor.
As with servers, personal computers that come with Linux already installed are available from vendors including Hewlett-Packard and Dell, although generally only for their business desktop lines.
On embedded devices, Linux is typically held in the device's firmware and may or may not be consumer-accessible.

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

[edit] 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 enable 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.

[edit] Installation through an existing platform

Most recently, a Windows installer for Ubuntu Linux was developed. This allows for one to download and install a Linux distribution without the need for a hard drive partition or the need for an installation CD, thus allowing for the option to easily dual boot between either operating system on the same hard drive without losing data. This was followed by the release of a Windows installer for Debian. Neither projects have been expressly endorsed by the vendors of either distribution as of January 2007.

[edit] Proprietary software

Some specific proprietary software products are not available in any form for Linux. This includes many popular computer games, although in recent years some game manufacturers have begun making their software available for Linux. For example, Epic Games sells a Linux version of its Unreal Tournament 2004. This problem is also addressed by emulation and API-translation projects like Wine and Cedega, which make it possible to run non-Linux-based software on Linux systems, either by emulating a proprietary operating system or by translating proprietary API calls (e.g., calls to Microsoft's Win32 or DirectX APIs) into native Linux API calls.

[edit] OEM Contracts

Computer hardware is often sold with the operating system of a software original equipment manufacturer (OEM) already installed. It is uncommon for this operating system to be Linux, even though the portability features of Linux mean that it can be installed on most machines. In the case of IBM PC compatibles the OS is usually Microsoft Windows; in the case of Apple Macintosh computers it has always been a version of Apple's OS, currently Mac OS X; Sun Microsystems sells SPARC hardware with Solaris installed; video game consoles such as the Xbox, PlayStation, and Gamecube each have their own proprietary OS. That Linux is not installed by default on most computer hardware limits its market share: consumers are unaware that an alternative exists, they must make a conscious effort to use a different operating system, and they must either perform the actual installation themselves, or depend on support from a friend, relative, or computer professional.

However, it is actually possible to buy hardware with Linux pre-installed. Hewlett-Packard and Dell both sell general purpose Linux laptops,^[10] and custom-order PC manufacturers will also build Linux systems. Terra Soft sells Macintosh computers and PlayStation 3 consoles with Yellow Dog Linux pre-installed. It is more common to find embedded devices sold with Linux as the default manufacturer-supported OS, including the Linksys NSLU2 NAS device, TiVo's line of personal video recorders, and Linux-based cellphones, PDAs, and portable music players.

Consumers also have the option of obtaining a refund for unused OEM operating system software. The end user license agreement (EULA) for Apple and Microsoft operating systems gives the consumer the opportunity to reject the license and obtain a refund. If requesting a refund directly from the manufacturer fails, it is also possible that a lawsuit in small claims court will work.^[11] On February 15, 1999, a group of Linux users in Orange County, California held a "Windows Refund Day" protest in an attempt to pressure Microsoft into issuing them refunds.^[12] In France, the Linuxfrench and AFUL organizations along with free software activist Roberto Di Cosmo started a "Windows Detax" movement,^[13] which led to a 2006 petition against "racketiciels"^[14] (translation: software racketeers) and the DGCCRF branch of the French government filing several complaints against bundled software.