lsg01.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

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<P>X (sometimes improperly called X Windows) is a graphical user interface(GUI) designed at MIT to provide portable GUI applications across different platforms. The version of X supplied with Linux is called XFree86 and is a direct port of the standard X11R5 system to 80386-based architectures. (Updates to the latest version of X, called X11R6, are beginning to appear, too.) XFree86 has been extended to provide compatibility with some other GUIs, including Open Look.



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<P>XFree86 supports several different video cards at a number of resolutions, offering a high-resolution graphical interface. Any X application can be recompiled to run properly under Linux, and a number of games, utilities, and add-ons have been developed and supplied as part of the X system. The XFree86 system also includes application development libraries, tools, and utilities. With these features, programmers can write applications specifically for X without having to invest in expensive software development kits or libraries.



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<FONT SIZE=4 COLOR="#FF0000"><B>DOS Interface</B></FONT></CENTER></H4>



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<P>Because Linux is designed for PCs, some compatibility with Microsoft MS-DOS is naturally part of the operating system. Linux provides a DOS emulator, which allows many DOS applications to be executed directly from within Linux, as part of the distribution system. Don't expect complete portability of DOS applications, though, as some applications are written to access peripherals or disk drives in a manner that Linux can't handle. The WINE (WINdows Emulator) project has developed a Microsoft Windows emulator for Linux, which enables Windows applications to be run from within Linux.



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<P>Although Linux can emulate DOS and Windows, the emulation feature is not intended to support full DOS usage. Instead, it provides the occasional DOS user with the ability to run an application under Linux. For heavy DOS use, your system should be set up with both DOS and Linux in separate partitions, enabling you to enter either one at boot time. <A HREF="lsg02.htm">Chapter 2</A> explains how to set this up.



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<P>Linux does allow you to transfer files seamlessly between the Linux filesystem and DOS by accessing the DOS partitions on a hard disk directly, if so configured. This capability makes it easy to move files and applications back and forth between the two operating systems.



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<FONT SIZE=4 COLOR="#FF0000"><B>TCP/IP</B></FONT></CENTER></H4>



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<P>TCP/IP (Transmission Control Protocol/Internet Protocol) is the primary networking system used by UNIX and Linux. TCP/IP is a full family of protocols that were developed for the Internet, and you must use TCP/IP when you venture out onto the Internet. If you want to connect with other UNIX machines, you will probably have to use TCP/IP as well. The Linux TCP/IP implementation provides all the networking software and drivers usually associated with a commercial UNIX TCP/IP package. With this implementation, you can create your own local area network(LAN), attach to existing Ethernet LANs, or connect to the Internet.



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<P>Networking is a strong feature of Linux, and will be dealt with in considerable detail later in this book. You don't have to network your Linux system, of course, but a network is cheap and simple to install and is a fantastic method for transferring files between systems. You can network over modems, too, so you can have your friends' Linux machines on a network.



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<FONT SIZE=5 COLOR="#FF0000"><B>Linux's History</B></FONT></CENTER></H3>



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<P>Linux was developed as a freely distributable version of UNIX. UNIX is the most widely used operating system in the world and has long been the standard for high-performance workstations and larger servers. UNIX, first developed in 1969, has a strong programmer-oriented user group that supports the operating system.



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<NOTE>How did UNIX get its name? It was based on an operating systems called MULTICS (MULTiplexed Information and Computing System). Ken Thompson, Dennis Ritchie, and Brian Kernighan were involved the design of a new operating system based on MULTICS that would be much simpler. They called the new operating system UNICS (Uniplexed Information and Computing System), which was quickly changed to UNIX.</NOTE>



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<P>Because UNIX is a commercial product, it must be bought for each platform it runs on. Licensing fees for UNIX versions for PC machines range from a few hundred dollars to several thousand. In an attempt to make UNIX widely available for no cost to those who want to experiment with it, a number of public domain UNIX systems have been developed over the years.



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<P>One of the early UNIX workalikes was Minix, written by Andy Tanenbaum. Although Minix didn't have a full range of features, it provided a small operating system that could be used on PC machines. To expand on Minix, a number of users started developing an enhanced operating system that would take advantage of the 80386 CPU's architecture. One of the primary developers of this system, which became known as Linux, was Linus Torvalds of the University of Helsinki. He released an early version of Linux in 1991. A first commercial, almost bug-free release was unleashed to the programming community in March 1992.



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<P>Soon, many programmers were working on Linux, and as the challenge and excitement of producing a growing UNIX workalike caught on, Linux grew at a remarkable rate. As the number of developers working on Linux grew, the entire UNIX workalike operating system was eventually completed and now includes all the tools you will find in a commercial UNIX product. Linux continues to grow as programmers adapt features and programs that were originally written as commercial UNIX products to Linux. New versions of Linux and its utilities are appearing at an astounding rate. New releases often appear weekly.



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<P>To avoid any charges for Linux, the Linux developers do not use any code from other UNIX systems. There are no licensing fees involved with the Linux operating system, and part of its mandate is to be freely available. Some companies have undertaken the task of assembling and testing versions of Linux, which they package on a CD-ROM for a (usually) minimal price.



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<P>Linux is not based on a single version of UNIX; it is a consolidation of the best features of BSD UNIX and System V. BSD UNIX was developed at the University of California at Berkeley, starting in 1977. Several major releases increased the power of BSD UNIX. Several standard UNIX programs originated at BSD, although BSD stopped its UNIX development in the early 1990s. AT&amp;T, which developed the first version of UNIX, continued their UNIX development by producing a series of UNIX versions called System III, System IV, and System V. Linux uses the last primary release of BSD UNIX called 4.4BSD as its base and takes some other features from the latest release of System V, called System V Release 4 (SVR4).



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<FONT SIZE=5 COLOR="#FF0000"><B>Copyrights</B></FONT></CENTER></H3>



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<P>Just because Linux is distributed for free, it doesn't mean the software is not copyrighted. Linux has been registered as copyrighted under the GNU General Public License (GPL), which is known in the programming community as a copyleft instead of copyright because of its nature. The GPL allows you to redistribute the Linux software, along with the complete source code, to anyone who wants it. However, the original owner of the components retains the copyrights to the software.



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<P>Linux doesn't have any kind of warranty. Even if you buy the Linux software from someone and pay them for maintenance, you cannot ever pursue the Linux programmers. They make no statement of functionality. If Linux destroys all your accounting or database data, it's tough luck. You assume the risk. That having been said, Linux has proven itself very stable and no incidents of serious data damage have occurred as a result of its programming. However, if the chance that something may go wrong is too great a risk for your business, you may be better off buying a commercial UNIX system that does have a warranty.



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<P>According to the GNU GPL, you can even sell Linux. You can modify any of the code, and repackage it as you want. You do not own the software and cannot claim copyright, however, even if you have modified the source code. The GNU GPL also imposes one condition on the sale of Linux&#151;you must provide all source code with the system if you sell it for profit so that others can further modify and sell it, too.



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<P>The authors and developers of Linux don't receive any royalties or shareware fees. For the most part, they provide the software to end users for the true love of programming and sharing their code with other programmers who appreciate it.



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<FONT SIZE=5 COLOR="#FF0000"><B>Sources of Help</B></FONT></CENTER></H3>



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<P>Linux does not have a telephone support line. In one sense, you are on your own when you install Linux. On the other hand, many thousands of Linux users are willing to help everyone from neophyte to experienced programmer. All you have to know is where to look for help. The two sources of help are written documentation and the user community.



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<FONT SIZE=4 COLOR="#FF0000"><B>Documentation</B></FONT></CENTER></H4>



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<P>The first exposure most people get to Linux is the Linux INFO-SHEET, a relatively short ASCII document that is available from USENET, BBSs (bulletin board systems), and many user groups. The INFO-SHEET is a quick summary of Linux. It is posted at regular intervals to the Linux newsgroups on USENET.



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<P>As Linux was developed, several programmers started writing brief guides to their contributions as well as wider areas of the operating system. Although these documents were usually terse and awkward to read, they did provide others with enough information to continue using Linux. Over a short span of time, the documentation for Linux grew rapidly and a central organizing body was needed to help keep it on track and avoid duplication.



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<P>The Linux Documentation Project was created to provide a complete set of public domain documentation for Linux. From a few rough installation notes a couple of years ago, the documentation has expanded to include almost a thousand pages, some very good, some not. The following primary documents are currently available or soon to be released:



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<LI><I>Linux Installation</I> explains how to install and configure Linux.



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<LI>The <I>Linux User's Guide</I> is a guide for first-time users.



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<LI>The <I>Linux System Administrator's Guide</I> is a guide to various aspects of system administration.



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<LI>The <I>Linux Network Administration Guide</I> explains how to set up and use networks.



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<LI>The <I>Linux Kernel Hacker's Guide</I> is a guide to modifying the Linux kernel.



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<P>In addition to these primary documents, there are about a dozen smaller guides to specific or esoteric aspects of Linux. These smaller guides are called How To documents. Together they form a growing document suite that covers practically every aspect of Linux. These documents are available with most distributions of the software. Not all the documents are up to date, as changes to the operating system have occurred since they were first written. Several different people wrote the Linux documents, so the styles and layout are not consistent. A perfect-bound printed copy of the Linux Documentation Project is available from Linux Systems Labs and some bookstores.



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<NOTE>You can contact Linux Systems Labs at 49884 Miller Ct., Chesterfield, MI 48047. Their telephone number is [phone], and their fax machine number is [phone]. You can get information about LSL from their e-mail address <A HREF="mailto:[e-mail]">[e-mail]</A>.</NOTE>



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<P>A number of Frequently Asked Questions (FAQ) files are available through the Linux newsgroups on USENET and as part of the distribution set. The FAQs tend to be quick problem-solving items, designed to save you from thumbing through many pages of on-line documentation. One FAQ called the META-FAQ provides basic information about Linux, where to get it, and the documentation that goes with it. It too is regularly posted to newsgroups.



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<P>A file called the Linux Software Map (LSM) contains a list of many of the components in Linux. Unfortunately, the LSM is incomplete and lacks considerable chunks of data. However, it is a good starting point if you want to see what is included with Linux. The LSM is updated at intervals and can be obtained from USENET, a Linux FTP site, or with a distribution set.



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<P>Finally, Linux mailing lists are available to anyone with e-mail access to the Internet. Information on the Linux mailing lists (there are quite a few) is available from USENET newsgroups or BBSs. See the appendixes for more information about the newsgroups, BBSs, and FTP sites.



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<FONT SIZE=4 COLOR="#FF0000"><B>USENET Newsgroups</B></FONT></CENTER></H4>