lsg01.htm

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

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<H2>Linux System Administrator's Survival Guide lsg01.htm</H2>



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<A HREF="#E68E1" >What Is Linux?</A>



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<A HREF="#E69E1" >Linux's Kernel</A>



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<A HREF="#E69E2" >GNU software</A>



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<A HREF="#E69E3" >X</A>



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<A HREF="#E69E4" >DOS Interface</A>



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<A HREF="#E69E5" >TCP/IP</A></UL>



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<A HREF="#E68E2" >Linux's History</A>



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<A HREF="#E68E3" >Copyrights</A>



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<A HREF="#E68E4" >Sources of Help</A>



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<A HREF="#E69E6" >Documentation</A>



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<A HREF="#E69E7" >USENET Newsgroups</A>



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<A HREF="#E69E8" >World Wide Web Sites</A>



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<A HREF="#E69E9" >Linux Journal</A></UL>



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<A HREF="#E68E5" >Recent Linux Distributions</A>



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<A HREF="#E68E6" >Summary</A></UL></UL></UL>



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<FONT SIZE=6 COLOR="#FF0000"><B>Chapter 1</B></FONT></CENTER></H1>



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<FONT SIZE=6 COLOR="#FF0000"><B>Introduction to Linux</B></FONT></CENTER></H2>



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<P>The Linux operating system has become immensely popular. USENET newsgroups dedicated to the Linux operating system have hundreds of messages a day, CD-ROMs of Linux archives are sold by the thousands, and even more DOS users are wandering around trying to figure out UNIX syntax and Linux installation problems. In many ways, the interest in Linux brings back the heady hacker days and the excitement of CP/M and early DOS machines.



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<P>Linux does have its problems though. One problem is the wide variety of Linux versions available, some of which are not very stable. The quality of the installation and configuration utilities also varies widely from Linux version to Linux version. Another problem is supporting documentation. Although this problem is decreasing as more people get involved, most available Linux documentation can be intimidating for first-time users (and some veterans). Commercial books dedicated to beginning Linux users are helping by offering a smoother explanation, but most books are simply rehashed Linux documents.



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<P>Although this book also uses the Linux documentation as a basis, it also uses almost two decades of UNIX system administration experience, years of working with Linux, and a lot of advice from other users. This book is not designed for a new Linux user who can't find their way around a filesystem, although readers with any knowledge of UNIX will feel quite at home. Instead, this book is for Linux users who want to expand their systems, optimize them, and learn more about system administration.



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<NOTE>Two schools of thought exist on pronouncing <I>Linux</I>. Because Linux is similar to UNIX and was originally developed by a programmer with the first name Linus, many assume the long <I>i</I>, as in <I>line-ucks</I>, is correct. On the other hand, Linux was developed to replace a UNIX workalike called Minix (with a short <I>i</I>), so the rest of the Linux community calls the operating system <I>lih-nicks</I>. Which is correct? The original developers used the latter pronunciation, while most North Americans prefer the former. Choose whichever you wish.</NOTE>



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<FONT SIZE=5 COLOR="#FF0000"><B>What Is Linux?</B></FONT></CENTER></H3>



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<P>Linux is a freely distributed, multitasking, multiuser operating system that behaves like UNIX. Designed specifically for the PC, Linux takes advantage of the PC's architecture to give you performance similar to UNIX workstations of a couple of years ago. Linux isn't a small, simple operating system like DOS (even in its latest incarnations). The development of UNIX has resulted in a mish-mash of files and directories, all of which are carried over to Linux for compatibility and programming reasons.



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<P>Linux includes a bunch of files for the operating system itself (called the kernel), a ton of utility programs, documentation files, add-on emulators for other operating systems, and much more. The following sections explain what you get when you install Linux on your system. Future chapters expand on these topics.



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<FONT SIZE=4 COLOR="#FF0000"><B>Linux's Kernel</B></FONT></CENTER></H4>



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<P>Linux is a complete multitasking, multiuser operating system that behaves like the UNIX operating system in terms of kernel behavior and peripheral support. Linux has all the features of UNIX, plus several recent extensions that add new versatility to Linux. All source code for Linux and its utilities is freely available.



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<P>The Linux kernel was originally developed for the Intel 80386 CPU's protected mode. The 80386 was designed with multitasking in mind (despite the fact that most of the Intel CPUs are used with single-tasking DOS), and Linux makes good use of the advanced features built into the CPU's instruction set. Memory management is especially strong with the 80386 (compared to earlier CPUs). A floating-point emulation routine allows Linux to function on machines that do not have math coprocessors (such as the SX series of Intel CPUs).



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<P>Linux allows shared executables so that if more than one copy of a particular application is loaded (either by one user running several identical tasks, or several users running the same task), all the tasks can share the same memory. This process, called copy-on-write pages, makes for much more efficient use of RAM.



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<P>The Linux kernel also supports demand paging, which means that only sections of a program that are necessary are read into RAM. To further optimize memory usage, Linux uses a unified memory pool. This pool enables all free memory on the system to be used as disk cache, effectively speeding up access to frequently used programs and data. As memory usage increases, the amount of cache is automatically adjusted.



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<P>To support large memory requirements when only small amounts of physical RAM are available, Linux supports swap space. Swap space enables pages of memory to be written to a reserved area of a disk and treated as an extension of physical memory. By moving pages back and forth between the swap space and RAM, Linux can effectively behave as if it had more physical RAM than it does, albeit at the cost of some speed due to the hard drive's slower access.



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<P>Linux uses dynamically shared libraries extensively. Dynamically shared libraries use a common library section for many different applications, effectively reducing the size of each application. Linux does allow full library linking (called statically linked libraries) for portability to machines that may not have the dynamic libraries.



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<P>To make Linux widely acceptable, it supports a number of different filesystems, including those compatible with DOS and OS/2. Linux's own primary filesystem, called ext2fs, is designed for optimal use of the disk.



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<P>Linux is ideally suited for application development and experimentation with new languages. Several different compilers, including C, C++, Fortran, Pascal, Modula-2, LISP, Ada, Basic, and Smalltalk, come with the distribution software. Many of the Linux compilers, tools, debuggers, and editors are from the Free Software Foundation's GNU project.



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



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<P>GNU (a recursive acronym for Gnu's Not UNIX) was developed by the Free Software Foundation(FSF) to provide royalty-free software to programmers and developers. Since it was created, many programmer packages and toolkits have been developed and assigned to FSF for distribution. Most of the GNU software mirrors(and often improves upon) commercially available software.



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<P>Linux includes many GNU utilities, including the languages mentioned earlier, debuggers, and compiler tools. Text processors, print utilities, and other GNU tools are also included with most Linux distributions. As more software becomes available from FSF, it can be ported and compiled under Linux because Linux behaves as a standard UNIX operating system.



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