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Short History of Linux

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					    1            Overview of UNIX and
                 Linux


            In This Chapter
               A Short History of UNIX and Linux
               Similarities and Differences UNIX/Linux Systems
               Command-line Interfaces versus Graphical Interfaces
               Why UNIX or Linux?
               Summary
               Exercises




    T
           his chapter provides a brief background of UNIX® and Linux®, and explains
           the motivation behind the contents of the rest of the book. Beginning with a
           brief description of the common UNIX and Linux systems, you will learn
    why these systems are important as compared to non-UNIX and non-Linux oper-
    ating systems. The chapter concludes with an explanation of graphical and non-
    graphical interfaces and environments.


A SHORT HISTORY OF UNIX AND LINUX

    In the early 1960s, the first computing operating systems were designed to allow
    only a single user to run one program at a time. This meant that the computing sys-
    tem was restricted in use for one person at a given time. Moreover, if more than one

                                                                                      1
2   Introduction to UNIX/Linux



    person needed to use the system, each person needed to schedule a specific time to
    use the system. In addition, the user could issue only one computer task at a time
    and waited for the task to complete before issuing another task. These restrictions
    greatly limited the operation and employment of these very expensive computing
    systems. As a result, only large businesses, educational institutions, and govern-
    mental agencies could afford to use them.
         Over time, more people needed to do their work on computers, along with an
    increasing number of tasks. Consequently, there was an overwhelming need for a
    computing system that could support not only multiple users at a time, but also
    could handle multiple tasks or programs at a time. To address these pressing needs,
    the Multics Project, which means Multiplexed Information and Computing Service
    (Multics), was created to help design and develop a multiuser system. The Multics
    Project brought together many prominent businesses and educational institutions,
    including AT&T, the Massachusetts Institute of Technology, and General Electric.
    After a few years, the project created a prototype multiuser system that could sup-
    port several users simultaneously. But it failed to achieve many of its original grand
    goals and the project was disbanded in the late 1960s.
         After the breakup of the Multics Project, some of its more visionary members,
    notably K. Thompson, D. M. Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to
    develop a system independently based on many of the Multics concepts. The out-
    come was UNIX—a multiuser, multitasking operating system. As a result of their
    efforts, the C programming language was developed to facilitate the development
    and eventual portability of UNIX onto new hardware. By the mid 1970s, AT&T re-
    alized these farsighted individuals had created a functional multiuser and multi-
    tasking system, and regained interest. Over the next decade or so, AT&T provided
    UNIX systems to various education institutions and businesses.
         Because UNIX was designed to be both a multiuser and an interactive time-
    sharing operating system, other computing manufacturers developed and sold cus-
    tom versions of UNIX designed specifically for their own computing systems. Some
    of these manufacturers and their systems included IBM’s developed version, AIX®;
    Hewlett Packard’s version, HP-UX®; and Sun Microsystems’s versions, SunOS®
    and Solaris®.
         In 1991, Linus Torvalds announced he developed a PC-based system called
    Linux, which functioned as the large UNIX systems installed by the major hardware
    vendors. Linux targeted PC hardware, which was inexpensive, readily available,
    and numerous. Because of the open source nature of Linux, which meant its source
    code was freely available and sharable between users and machines, it gave Linux’s
    users the ability to modify the functionality of source code as desired. The Linux
    audience grew to include a large number of technical users worldwide, who pro-
    vided new source code that added to the system, fixed “bugs,” optimized perfor-
    mance, and provided support for various hardware platforms. Linux versions soon
                                                      Overview of UNIX and Linux        3


    became available for non-PC systems as well, allowing for its use on virtually any
    platform or hardware combination.


SIMILARITIES AND DIFFERENCES OF UNIX/LINUX SYSTEMS

    In this book, the term UNIX/Linux refers to UNIX and Linux systems in general.
    Any UNIX/Linux system will provide the same basic concepts, such as files, direc-
    tories, permissions, jobs, processes, redirection, and piping, which are discussed in
    the following chapters. This book focuses on the major features and commands
    common to nearly all UNIX/Linux systems, meeting the needs of most users.
         While each UNIX/Linux system uses many common concepts, the look or feel
    of each system may vary; some variations depend on how commands or utilities are
    installed or how accounts are configured on the system. A command usually refers
    to a simple task that is built in to an interface—a program or device that controls
    the way equipment or programs work together—such as navigating to different di-
    rectories in a filesystem. An application or utility refers to a program or software
    package that accomplishes certain tasks, such as creating a backup collection of files
    or viewing system performance. Certain commands and applications are found on
    any UNIX/Linux system, and you will learn more about these in later chapters.
         Many factors affect which commands or utilities are available. One such factor
    is the role of the system. For example, a programming system typically provides all
    applications needed to compile, debug, and optimize a program, whereas a Web
    server may not, if the policies of a business or educational institution predetermine
    the selection of commands or utilities available. Typically, users select an interface
    and how that it is used. See Chapter 3, “Getting Started with UNIX/Linux” and
    Chapter 11, “Basic Account and System Maintenance,” for further information.
         Another difference among systems involves the appearance of the environment
    and the ways users issue operations. These differences are also affected by the role
    of the system or what applications are installed.


COMMAND-LINE INTERFACE VERSUS GRAPHICAL INTERFACES

    A user interacts with the computing system using a keyboard, mouse, or both. A
    command-line interface needs commands typed in via a keyboard and a graphical
    interface (also called a graphical user interface or GUI) uses icons activated by a
    mouse click. Sometimes a graphical interface requires keyboard input, such as en-
    tering a filename. These interfaces change the look and layout of a program on the
    screen or the system itself for interaction with the user.
4   Introduction to UNIX/Linux



         Evolving simplification of computing hardware promotes icon popularity, but
    this does not mean command-line interfaces are no longer important. On the con-
    trary, the range of operations a user can initiate by pointing and clicking a mouse
    is much smaller than by using keyboard commands. Understanding this can be
    vital when you need a command to accomplish a task in a specific manner.
         Many times a command-line interface is a more efficient and preferred ap-
    proach. For example to specify a filename with a command-line interface, you sim-
    ply type the filename. To specify a filename with a graphical interface, you must
    point, click (possibly multiple times), and then key in the information. The addi-
    tional hand movements needed to change from keyboard to mouse can be fatigu-
    ing and time consuming.
         In addition, some machines have a dedicated function that limits its use. A
    business or institution policy may limit which applications a machine can run or
    provide to a user. For example, a file, Web, or database server may be responsible
    for high-traffic volumes or fast responses. A policy may dictate that the system not
    use a graphical environment or a mouse, as these features increase the workload for
    the machine, consequently, hampering its ability to attend to its responsibilities.
         Moreover, if you access another machine over the network, as you will learn in
    Chapter 12, “Network-Based Utilities,” command-line interfaces are often how
    you interact with that other computer system.
         The focus of this book is on command lines that are similar and available across
    the various UNIX/Linux systems, however, interfaces that use graphics are not ig-
    nored. On the contrary, graphical interfaces provide command-line interfaces
    within a terminal (workstation visual display) window, as explained more com-
    pletely in Chapter 3. It is actually common for a user to have a graphical interface
    on their system along multiple open command-line terminal windows, so each
    command line can be used for different work.


WHY UNIX/LINUX?

    UNIX and Linux are examples of operating systems, or system-level software that
    contains the necessary support to use and manage the CPU, disk, monitor, and
    other hardware. An operating system controls the hardware and contains the sup-
    port to load and run application software to create documents, write programs,
    manipulate graphics, surf the Internet, or accept user commands. In simple terms,
    application software is a program you use to create documents, draw figures, and
    accomplish other work. To recap, a computer operating system controls and runs
    the basic software operating on a computer, underneath things like word proces-
    sors and spreadsheets, and controls all the hardware in an organized and pre-
    dictable way.
                                                       Overview of UNIX and Linux         5


         While other operating systems are available, UNIX or Linux is often preferred
    for its reliability, security, and speed. Many businesses demand their critical sys-
    tems, such as databases, file servers, Web servers, and production servers run on
    UNIX or Linux. Because UNIX and Linux systems have been around for several
    years, many bugs and security issues have been discovered and resolved. UNIX and
    Linux systems are also able to survive and continue operating after a failure of a
    hardware component such as a disk, CPU, or network connection.
         Many academic environments—particularly those in technical fields and at the
    graduate level—use UNIX or Linux for their work. UNIX and Linux systems pro-
    vide a number of ways to accomplish sophisticated tasks, such as analyzing pro-
    gram performance and changing or adding operating system functionality.
    Academic environments not only favor UNIX or Linux because of these features
    and its reliability, but also to provide their students exposure to a system that they
    may very well use in the workplace.
         Open Source Linux systems and software are also attractive choices because of
    their low (or no) cost and extensive support benefits. A system or piece of software
    that is open source is generally free to use, and easily available by Internet download.
    A large team of technical users create updates (fixes) and make them available to
    other open source users.
         Because of the many features and benefits of Linux, you can use the compan-
    ion software to install and learn. The discussion is general enough for most, if not
    all, UNIX/Linux systems. If you wish to install and use this provided system, please
    refer to Chapter 2, “Installing a Linux (Fedora™) System.”


SUMMARY

    This chapter provided a brief history about the evolution of UNIX/Linux. Differ-
    ences between the UNIX/Linux systems currently in use were explained, as well as
    an overview of how they may be used. A description of the book’s focus and pur-
    pose was explained and various UNIX/Linux concepts were demonstrated, in a
    manner intended to accommodate the widest audience and variety of uses possible.


EXERCISES

         1. What are the differences between a command-line interface and a graphi-
            cal interface?
         2. How are UNIX systems and Linux systems different?
         3. What are some reasons that one may choose UNIX/Linux over some other
            operating system?
6   Introduction to UNIX/Linux



         4. Using on-line resources, find some UNIX systems. Give the name for each
            of those systems as well as the company(s) that provide each system.
         5. Using on-line resources, find some Linux systems. Give the name for each
            of those systems as well as the company(s) that provide each system.

				
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