Linux video: understanding linux kernel

This article is about operating systems that use the Linux kernel. For the kernel itself, see Linux kernel. For other uses, see Linux (disambiguation).

**Linux**
Tux, the penguin, mascot of the Linux kernel
OS family:	Unix-like
Latest stable release:	2.6.22.1 (Linux kernel) / July 10, 2007
Kernel type:	Monolithic kernel
License:	Kernel: GNU General Public License/various
Working state:	Current

Linux
History
GNU Project • Linux kernel (history • portability and supported architectures) • Naming controversy • Windows and Linux • Adoption • Linus's Law • Tux • SCO and Linux
Distribution
Linux distribution (list • comparison) • Linux package formats • LiveDistro (list • comparison) • Live USB • Mini Linux
Applications
Server • Desktop • Embedded • Gaming • Thin client This box: view • talk

Linux (IPA pronunciation: /ˈlɪnʊks/) is a Unix-like computer operating system. Linux is one of the most prominent examples of free software and open source development; its underlying source code can be freely modified, used, and redistributed by anyone.^[1]

The Linux kernel was first released to the public on 17 September 1991, for the Intel x86 PC architecture. The kernel was augmented with system utilities and libraries from the GNU project to create a usable operating system, which later led to the alternate term GNU/Linux.^[2] Linux is now packaged for different uses in Linux distributions, which contain the sometimes modified kernel along with a variety of other software packages tailored to different requirements.

Predominantly known for its use in servers, Linux has gained the support of corporations such as IBM^[3], Sun Microsystems^[4], Dell^[5], Hewlett-Packard^[6], and Novell^[7], and is used as an operating system for a wide variety of computer hardware, including desktop computers, supercomputers,^[8] and embedded devices such as mobile phones and routers.

Philosophy

The primary difference between Linux and many other popular contemporary operating systems is that the Linux kernel and other components are free and open source software. Linux is not the only such operating system, although it is the most well-known and widely used one. Some free and open source software licences are based on the principle of copyleft, a kind of reciprocity: any work derived from a copyleft piece of software must also be copyleft itself. The most common free software license, the GNU GPL, is used for the Linux kernel and many of the components from the GNU project.

As an operating system underdog competing with mainstream operating systems, Linux cannot rely on a monopoly advantage; in order for Linux to be convenient for users, Linux aims for interoperability with other operating systems and established computing standards. Linux systems adhere to POSIX,^[32] SUS,^[33] ISO, and ANSI standards where possible, although to date only one Linux distribution has been POSIX.1 certified, Linux-FT.^[34]

Linux is a widely ported operating system. While the Linux kernel was originally designed only for Intel 80386 microprocessors, it now runs on a more diverse range of computer architectures than any other operating system—from the hand-held ARM-based iPAQ to the mainframe IBM System z9, in devices ranging from supercomputers to mobile phones.^[35] Specialized distributions exist for less mainstream architectures. The ELKS kernel fork can run on Intel 8086 or Intel 80286 16-bit microprocessors, while the µClinux kernel may run on systems without a memory management unit. The kernel also runs on architectures that were only ever intended to use a manufacturer-created operating system, such as Macintosh computers, PDAs, Video game consoles, portable music players, and Mobile phones.

Linux is largely driven by its developer and user communities. Some vendors develop and fund their distributions on a volunteer basis, Debian being a well-known example. Others maintain a community version of their commercial distributions, as RedHat does with Fedora.

In many cities and regions, local associations known as Linux Users Groups (LUGs) seek to promote Linux and by extension free software. They hold meetings and provide free demonstrations, training, technical support, and operating system installation to new users. There are also many internet communities that seek to provide support to Linux users and developers. Most distributions and open source projects have IRC chatrooms or newsgroups. Online forums are another means for support, with notable examples being LinuxQuestions.org and the Gentoo forums. Linux distributions host mailing lists; commonly there will be a specific topic such as usage or development for a given list.

There are several technology websites with a Linux focus. Linux Weekly News is a weekly digest of Linux-related news; the Linux Journal is an online magazine of Linux articles published monthly; Slashdot is a technology-related news website with many stories on Linux and open source software; Groklaw has written in depth about Linux-related legal proceedings; and there are many articles relevant to Linux on the Free Software Foundation website.

Although Linux is generally available free of charge, several large corporations have established business models that involve selling, supporting, and contributing to Linux and free software. These include Dell, IBM, HP, Sun Microsystems, Novell, and Red Hat. The free software licenses on which Linux is based explicitly accommodate and encourage commercialization; the relationship between Linux as a whole and individual vendors may be seen as symbiotic. One common business model of commercial suppliers is charging for support, especially for business users. A number of companies also offer a specialized business version of their distribution, which adds proprietary support packages and tools to administer higher numbers of installations or to simplify administrative tasks. Another business model is to give away the software in order to sell hardware.

The XO laptop project of One Laptop Per Child is creating a new and potentially much larger Linux community, planned to reach several hundred million schoolchildren and their families and communities in developing countries. Six countries have ordered a million or more units each for delivery in 2007 to distribute to schoolchildren at no charge. Google, Red Hat, and eBay are major supporters of the project.

History

See also: History of the Linux kernel

The Unix operating system was conceived and implemented in the 1960s and first released in 1970. Its wide availability and portability meant that it was widely adopted, copied and modified by academic institutions and businesses, with its design being influential on authors of other systems. One so-called Unix-like system was the GNU Project, started in 1984, had the goal of creating a POSIX-compatible operating system from entirely free software. In 1985, Richard Stallman created the Free Software Foundation and developed the GNU General Public License (GPLv1), in order to spread the software freely. Many of the programs required in an OS (such as libraries, compilers, text editors, a Unix shell, and a GUI) were developed by the early 1990s, so that most of the requirements for an operating system were complete, although low level elements such as device drivers, daemons, and the kernel were stalled and incomplete^[9]. Linus Torvalds has said that "If the GNU kernel had been ready last spring, I'd not have bothered to even start my project" ^[10].

Linus Torvalds, creator of the Linux kernel.

MINIX, a Unix-like system intended for academic use, was released by Andrew S. Tanenbaum in 1987. While source code for the system was available, modification and redistribution were restricted. In addition, MINIX's 16-bit design was not well adapted to the 32-bit design of the increasingly cheap and popular Intel 386 architecture for personal computers.

In 1991, Linus Torvalds began to work on a non-commercial replacement for MINIX while he was attending the University of Helsinki.^[11] This eventually became the Linux kernel.

Linux was dependent on the Minix userspace at first. With code from the GNU system freely available, it was advantageous if this could be used with the fledgling OS. Code licensed under the GNU GPL can be used in other projects, so long as they also are released under the same or a compatible license. In order to make the Linux kernel compatible with the components from the GNU Project, Torvalds initiated a switch from his original license (which prohibited commercial redistribution) to the GNU GPL.^[12] Linux and GNU developers worked to integrate GNU components with Linux to make a fully functional and free operating system.^[9]

Today Linux is used in numerous domains, from embedded systems^[13] to supercomputers,^[14] and has secured a place in server installations with the popular LAMP application stack.^[15] Torvalds continues to direct the development of the kernel. Stallman heads the Free Software Foundation, which in turn develops the GNU components. Finally, individuals and corporations develop third-party non-GNU components. These third-party components comprise a vast body of work and may include both kernel modules and user applications and libraries. Linux vendors combine and distribute the kernel, GNU components, and non-GNU components, with additional package management software in the form of Linux distributions.

Technorati Profile

Applications

Desktop

KDE 3.5, showing the Kontact personal information manager and Konqueror file manager, web browser, and file viewer.

Main article: Desktop Linux

Although in specialized application domains such as desktop publishing and professional audio there may be a lack of commercial quality software, users migrating from Mac OS X and Windows can find equivalent applications for most tasks.^[41]

Many free software titles that are popular on Windows are also available, such as Pidgin, Mozilla Firefox, Openoffice.org, and GIMP, amongst others. A growing amount of proprietary desktop software is also supported under Linux,^[42] examples being Adobe Flash Player, Acrobat Reader, Nero Burning ROM, Opera, RealPlayer, and Skype. In the field of animation and visual effects, most high end software, such as AutoDesk Maya, Softimage XSI and Apple Shake are available both for Linux, Windows and/or MacOS X. Additionally, CrossOver is a commercial solution based on the open source WINE project that supports running Windows versions of Microsoft Office and Photoshop.

See also: Linux gaming Servers and supercomputers
Historically, Linux has mainly been used as a server operating system, and has risen to prominence in that area; Netcraft reported in September 2006 that eight of the ten most reliable internet hosting companies run Linux on their web servers.^[43] This is due to its relative stability and long uptime, and the fact that desktop software with a graphical user interface is often unneeded. Enterprise and non-enterprise Linux distributions may be found running on servers. Linux is the cornerstone of the LAMP server-software combination (Linux, Apache, MySQL, Perl/PHP/Python) which has achieved popularity among developers, and which is one of the more common platforms for website hosting.

Linux is commonly used as an operating system for supercomputers. As of June 2007, out of the top 500 systems, 389 (77.8%) run Linux.^{[44]

Embedded devices}

Main article: embedded Linux

Due to its low cost and ability to be easily modified, an embedded Linux is often used in embedded systems. Linux has become a major competitor to the proprietary Symbian OS found in many mobile phones — 16.7% of smartphones sold worldwide during 2006 were using Linux^[45] — and it is an alternative to the dominant Windows CE and Palm OS operating systems on handheld devices. The popular TiVo digital video recorder uses a customized version of Linux.^[46] Several network firewall and router standalone products, including several from Linksys, use Linux internally, using its advanced firewall and routing capabilities. The Korg OASYS and the Yamaha Motif XS music workstations also run Linux.

Main articles: Linux adoption and Usage share of desktop operating systems

Many quantitative studies of open source software focus on topics including market share and reliability, with numerous studies specifically examining Linux.^[47] The Linux market is growing rapidly, and the revenue of servers, desktops, and packaged software running Linux is expected to exceed $35.7 billion by 2008.^[48] According to market research company IDC, 25% of servers and 2.8% of desktop computers ran Linux as of 2004.^[49]

The difficulty of measuring the exact number of deployments becomes apparent when looking at IDC's report for Q1 2007, which says that Linux now holds 12.7% of the overall server market.^[50] This estimate was based on the number of Linux servers sold by various companies, but since Linux servers are inherently free this number says nothing about the actual market share of the operating system, just how much money companies are making from selling it.

It has been alleged that people regard Linux as suitable mostly for computer experts because mainstream computer magazine reporters cannot explain what Linux is in a meaningful way, as they lack real life experience using it.^[51] Furthermore, the frictional cost of switching operating systems and lack of support for certain hardware and application programs designed for Microsoft Windows have been two factors that have inhibited adoption. However, as of early 2007, significant progress in hardware compatibility has been made, and it is becoming increasingly common for hardware to work “out of the box” with many Linux distributions. Proponents and analysts attribute the relative success of Linux to its security, reliability,^[52] low cost, and freedom from vendor lock-in.^[53]

Linux video

วันพฤหัสบดีที่ 26 กรกฎาคม พ.ศ. 2550

xvidcap test authority video

Philosophy

History

คลังบทความของบล็อก

เกี่ยวกับฉัน

ป้ายกำกับ

Applications