分类： LINUX
2008-11-02 10:55:02
Linux is an operating system that was initially created as a hobby by a young student, Linus Torvalds, at the University of Helsinki in Finland. Linus had an interest in Minix, a small UNIX system, and decided to develop a system that exceeded the Minix standards. He began his work in 1991 when he released version 0.02 and worked steadily until 1994 when version 1.0 of the Linux Kernel was released. The kernel, at the heart of all Linux systems, is developed and released under the GNU General Public License and its source code is freely available to everyone. It is this kernel that forms the base around which a Linux operating system is developed. There are now literally hundreds of companies and organizations and an equal number of individuals that have released their own versions of operating systems based on the Linux kernel. More information on the kernel can be found at our sister site, LinuxHQ and at the official Linux Kernel Archives. The current full-featured version is 2.6 (released December 2003) and development continues.
Apart from the fact that it's freely distributed, Linux's functionality, adaptability and robustness, has made it the main alternative for proprietary Unix and Microsoft operating systems. IBM, Hewlett-Packard and other giants of the computing world have embraced Linux and support its ongoing development. Well into its second decade of existence, Linux has been adopted worldwide primarily as a server platform. Its use as a home and office desktop operating system is also on the rise. The operating system can also be incorporated directly into microchips in a process called "embedding" and is increasingly being used this way in appliances and devices.
Throughout most of the 1990’s, tech pundits, largely unaware of Linux’s potential, dismissed it as a computer hobbyist project, unsuitable for the general public’s computing needs. Through the efforts of developers of desktop management systems such as KDE and GNOME, office suite project OpenOffice.org and the Mozilla web browser project, to name only a few, there are now a wide range of applications that run on Linux and it can be used by anyone regardless of his/her knowledge of computers. Those curious to see the capabilities of Linux can download a live CD version called Knoppix . It comes with everything you might need to carry out day-to-day tasks on the computer and it needs no installation. It will run from a CD in a computer capable of booting from the CD drive. Those choosing to continue using Linux can find a variety of versions or “distributions” of Linux that are easy to install, configure and use. Information on these products is available in our distribution section and can be found by selecting the mainstream/general public category.
HISTORY:
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.
The GNU Project, started in 1984, had the goal of creating a “complete Unix-compatible software system” made entirely of free software. In 1985, Richard Stallman created the Free Software Foundation and developed the GNU General Public License (GNU GPL). Many of the programs required in an OS (such as libraries, compilers, text editors, a Unix shell, and a windowing system) were completed by the early 1990s, although low level elements such as device drivers, daemons, and the kernel were stalled and incomplete. Linus Torvalds has said that if the GNU kernel had been available at the time (1991), he would not have decided to write his own.
MINIX
MINIX, a Unix-like system intended for academic use, was released by Andrew S. Tanenbaum in 1987. The source code for MINIX 1.0 was printed in his book Operating Systems: Design and Implementation. While easily available, modification and redistribution were restricted (although this is not the case today). The code was covered by the copyrights of the textbook, published by Prentice Hall. 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, Torvalds began to work on a non-commercial replacement for MINIX while he was attending the University of Helsinki. This eventually became the Linux kernel.
In 1992, Tanenbaum posted an article on Usenet claiming Linux was obsolete. In the article, he criticized the operating system as being monolithic in design and being tied closely to the x86 architecture and thus not portable, which he described as “a fundamental error”. Tanenbaum suggested that those who wanted a modern operating system should look into one based on the microkernel model. The posting elicited the response of Torvalds, which resulted in a well known debate over the microkernel and monolithic kernel designs.
Linux was dependent on the MINIX user space 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. Linux and GNU developers worked to integrate GNU components with Linux to make a fully functional and free operating system.
Design
Linux is a modular Unix-like operating system. It derives much of its basic design from principles established in Unix during the 1970s and 1980s. Linux uses a monolithic kernel, the Linux kernel, which handles process control, networking, and peripheral and file system access. Device drivers are integrated directly with the kernel.
Much of Linux’s higher-level functionality is provided by separate projects which interface with the kernel. The GNU userland is an important part of most Linux systems, providing the shell and Unix tools which carry out many basic operating system tasks. On top of the kernel, these tools form a Linux system with a graphical user interface that can be used, usually running in the X Window System.
User interface
Linux can be controlled by one or more of a text-based command line interface (CLI), graphical user interface (GUI) (usually the default for desktop), or through controls on the device itself (common on embedded machines).
On desktop machines, GNOME, KDE and Xfce are the most popular user interfaces, though a variety of other user interfaces exist. Most popular user interfaces run on top of the X Window System (X), which provides network transparency, enabling a graphical application running on one machine to be displayed and controlled from another.
Other GUIs include X window managers such as FVWM, Enlightenment, Fluxbox and Window Maker. The window manager provides a means to control the placement and appearance of individual application windows, and interacts with the X window system.
A Linux system usually provides a command line interface of some sort through a shell, which is the traditional way of interacting with a Unix system. A Linux distribution specialized for servers may use the CLI as its only interface. A “headless system” run without even a monitor can be controlled by the command line via a protocol such as SSH or telnet.
Most low-level Linux components, including the GNU Userland, use the CLI exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks, and provides very simple inter-process communication. A graphical terminal emulator program is often used to access the CLI from a Linux desktop.
Development
A summarized history of Unix-like operating systems showing Linux’s origins. Note that despite similar architectural designs and concepts being shared as part of the POSIX standard, Linux does not share any non-free source code with the original Unix or Minix.
A summarized history of Unix-like operating systems showing Linux’s origins. Note that despite similar architectural designs and concepts being shared as part of the POSIX standard, Linux does not share any non-free source code with the original Unix or Minix.
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 best-known and most widely used. 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 a form of copyleft, and is used for the Linux kernel and many of the components from the GNU project.
Linux systems adhere to POSIX, SUS, ISO and ANSI standards where possible. To date, however, only the Linux-FT distribution has been POSIX.1 certified.
Free software projects, although developed in a collaborative fashion, are often produced independently of each other. However, because the software licenses explicitly permit redistribution there is a basis for larger scale projects that collect the software produced by stand-alone projects and make this software available together in a Linux distribution.
A Linux distribution, commonly called a “distro”, is a project that manages a remote collection of Linux-based software, and facilitates installation of a Linux operating system. Distributions are maintained by individuals, loose-knit teams, volunteer organizations, and commercial entities. They include system software and application software in the form of packages, and distribution-specific software for initial system installation and configuration as well as later package upgrades and installs. A distribution is responsible for the default configuration of installed Linux systems, system security, and more generally integration of the different software packages into a coherent whole.
