In recent years Linux has emerged as a powerful and innovative UNIX work-alike. Its popularity is surpassing that of its UNIX predecessors. Although it mimics UNIX in many ways, the Linux operating system departs from UNIX in several significant ways: The Linux kernel is implemented independently of both BSD and System V, the continuing development of Linux is taking place through the combined efforts of many capable individuals throughout the world, and Linux puts the power of UNIX within easy reach of business and personal computer users. Using the Internet, today’s skilled programmers submit additions and improvements to the operating system to Linus Torvalds, GNU, or one of the other authors of Linux.
Applications. A rich selection of applications is available for Linux—both free and commercial—as well as a wide variety of tools: graphical, word processing, networking, security, administration, Web server, and many others. Large software companies have recently seen the benefit in supporting Linux and now have on-staff programmers whose job it is to design and code the Linux kernel, GNU, KDE, or other software that runs on Linux. For example, IBM (www.ibm.com/linux) is a major Linux supporter. Linux conforms increasingly more closely to POSIX standards, and some distributions and parts of others meet this standard. (See “Standards” on page 8 for more information.) These developments mean that Linux is becoming more mainstream and is respected as an attractive alternative to other popular operating systems.
Peripherals. Another aspect of Linux that appeals to users is the amazing range of peripherals that is supported and the speed with which support for new peripherals emerges. Linux often supports a peripheral or interface card before any company does. Unfortunately some types of peripherals—particularly proprietary graphics cards—lag in their support because the manufacturers do not release specifications or source code for drivers in a timely manner, if at all.
Software. Also important to users is the amount of software that is available—not just source code (which needs to be compiled) but also prebuilt binaries that are easy to install and ready to run. These include more than free software. Netscape, for example, has been available for Linux from the start and included Java support before it was available from many commercial vendors. Now its sibling Mozilla/Thunderbird/Firefox is also a viable browser, mail client, and newsreader, performing many other functions as well.
Platforms. Linux is not just for Intel-based platforms: It has been ported to and runs on the Power PC—including Apple computers (ppclinux), Compaq’s (née Digital Equipment Corporation) Alpha-based machines, MIPS-based machines, Motorola’s 68K-based machines, various 64-bit systems, and IBM’s S/390x. Nor is Linux just for single-processor machines: As of version 2.0, it runs on multiple-processor machines (SMPs). It also includes an O(1) scheduler, which dramatically increases scalability on SMP systems.
Emulators. Linux supports programs, called emulators, that run code intended for other operating systems. By using emulators you can run some DOS, Windows, and Macintosh programs under Linux. Wine (www.winehq.com) is an open-source implementation of the Windows API on top of the X Window System and UNIX/Linux; QEMU (www.nongnu.org/qemu) is a CPU-only emulator that executes x86 Linux binaries on non-x86 Linux systems.
Xen. Xen, which was created at the University of Cambridge and is now being developed in the open-source community, is an open-source virtual machine monitor (VMM). A VMM enables several virtual machines (VMs), each running an instance of a separate operating system, to run on a single computer. Xen isolates the VMs so that if one crashes it does not affect any of the others. In addition, Xen introduces minimal performance overhead when compared with running each of the operating systems natively.
Using VMs, you can experiment with cutting-edge releases of operating systems and applications without concern for the base (stable) system, all on a single machine. You can also set up and test networks of systems on a single machine. Xen presents a sandbox, an area (system) that you can work in without regard for the results of your work or for the need to clean up.
Fedora 12 includes Xen 3.4. This book does not cover the installation or use of Xen. See fedoraproject.org/wiki/Tools/Xen for installation instructions.
For more information on Xen, refer to the wiki at wiki.xensource.com/xenwiki and the Xen home page at www.cl.cam.ac.uk/research/srg/netos/xen.
Source of Information : Prentice Hall A.Practical Guide to Fedora and Red Hat Enterprise Linux 5th Edition
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