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144 lines
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<TITLE>Linux Information Sheet: Introduction to Linux</TITLE>
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<H2><A NAME="s1">1. Introduction to Linux</A></H2>
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<P>Linux is a completely free reimplementation of the POSIX specification,
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with SYSV and BSD extensions (which means it looks like Unix, but does
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not come from the same source code base), which is available in both
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source code and binary form. Its copyright is owned by Linus Torvalds
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<torvalds@transmeta.com> and other contributors, and is freely
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redistributable under the terms of the GNU General Public License (GPL).
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A copy of the GPL is included with the Linux source; you can also get a
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copy from
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<A HREF="ftp://prep.ai.mit.edu/pub/gnu/COPYING">ftp://prep.ai.mit.edu/pub/gnu/COPYING</A><P><B>Linux</B>, per se, is only the kernel of the operating system, the part
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that controls hardware, manages files, separates processes, and so forth.
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There are several combinations of Linux with sets of utilities and
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applications to form a complete operating system. Each of these
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combinations is called a <B>distribution</B> of Linux. The word <B>Linux</B>,
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though it in its strictest form refers specifically to the kernel, is
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also widely and correctly to refer to an entire operating system built
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around the Linux kernel. For a list and brief discription of various
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distributions, see
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<A HREF="http://sunsite.unc.edu/LDP/HOWTO/Distribution-HOWTO.html">http://sunsite.unc.edu/LDP/HOWTO/Distribution-HOWTO.html</A>
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<B>None</B> of these distributions is ``the official Linux''.
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<P>Linux is <B>not</B> public domain, nor is it `shareware'. It is `free'
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software, commonly called <B>freeware</B>
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or <B>Open Source Software[tm]</B> (see
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<A HREF="http://www.opensource.org">http://www.opensource.org</A>),
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and you may give away or sell
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copies, but you must include the source code or make it available in
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the same way as any binaries you give or sell. If you distribute any
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modifications, you are legally bound to distribute the source for those
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modifications. See the GNU General Public License for details.
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<P>Linux is still free as of version 2.0, and will continue to be free.
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Because of the nature of the GPL to which Linux is subject, it would be
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illegal for it to be made not free. Note carefully: the `free' part
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involves access to the source code rather than money; it is perfectly
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legal to charge money for distributing Linux, so long as you also
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distribute the source code. This is a generalization; if you want the
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fine points, read the GPL.
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<P>Linux runs on 386/486/Pentium machines with ISA, EISA, PCI and VLB busses.
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MCA (IBM's proprietary bus) is not well-supported in 2.0.x and earlier versions,
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but support has been added to the current development tree, 2.1.x.
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If you are interested, see
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<A HREF="http://glycerine.itsmm.uni.edu/mca">http://glycerine.itsmm.uni.edu/mca</A><P>There is a port to multiple Motorola 680x0 platforms
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(currently running on some Amigas, Ataris, and VME machines), which
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now works quite well. It requires a 68020 with an MMU, a 68030, 68040,
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or a 68060, and also requires an FPU. Networking and X now work.
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See
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<A HREF="news:comp.os.linux.m68k">news:comp.os.linux.m68k</A><P>Linux runs well on DEC's Alpha CPU, currently supporting the
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"Jensen", "NoName", "Cabriolet", "Universal Desktop Box" (better
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known as the Multia), and many other platforms. For more
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information, see
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<A HREF="http://www.azstarnet.com/~axplinux/FAQ.html">http://www.azstarnet.com/~axplinux/FAQ.html</A><P>Linux runs well on Sun SPARCs; most sun4c, sun4m, and sun4u machines now
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run Linux, with support for sun4 in development.
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Red Hat Linux is (as of this writing) the only
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Linux distribution available for SPARCs; see
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<A HREF="http://www.redhat.com/support/docs/rhl-sparc/">http://www.redhat.com/support/docs/rhl-sparc/</A><P>Linux is being actively ported to the PowerPC architecture,
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including PowerMac (Nubus and PCI), Motorola, IBM, and Be
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machines. See
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<A HREF="http://www.cs.nmt.edu/~linuxppc/">http://www.cs.nmt.edu/~linuxppc/</A> and
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<A HREF="http://www.linuxppc.org/">http://www.linuxppc.org/</A><P>Ports to other machines, including MIPS (see
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<A HREF="http://linus.linux.sgi.com">http://linus.linux.sgi.com</A> and
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<A HREF="http://lena.fnet.fr/">http://lena.fnet.fr/</A>)
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and ARM,
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are under way and showing various amounts of progress. Don't hold
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your breath, but if you are interested and able to contribute, you may
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well find other developers who wish to work with you.
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<P>Linux is no longer considered to be in beta testing, as version 1.0
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was released on March 14, 1994. There are still bugs in the system,
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and new bugs will creep up and be fixed as time goes on. Because
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Linux follows the ``open development model'', all new versions will
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be released to the public, whether or not they are considered
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``production quality''. However, in order to help people tell whether
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they are getting a stable version or not, the following scheme has
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been implemented: Versions n.x.y, where x is an even number, are
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stable versions, and only bug fixes will be applied as y is
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incremented. So from version 1.2.2 to 1.2.3, there were only bug
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fixes, and no new features. Versions n.x.y, where x is an odd number,
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are beta-quality releases for developers only, and may be unstable and
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may crash, and are having new features added to them all the time.
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>From time to time, as the currect development kernel stabilizes, it
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will be frozen as the new ``stable'' kernel, and development will
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continue on a new development version of the kernel. Note that most
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releases of the Linux kernel, beta or not, are relatively robust;
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``stable'' in this context means ``slow to change'' in addition
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to ``robust''.
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<P>The current stable version is 2.0.35 (this will continue to change as
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new device drivers get added and bugs fixed), and development has also
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started on the experimental 2.1.x kernels. The Linux kernel source code
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contains a file, Documentation/Changes, which explains changes that
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you should be aware of when upgrading from one kernel version to another.
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However, the great majority of Linux users simply update their Linux
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distribution occasionally to get a new kernel version.
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<P>Most versions of Linux, beta or not, are quite robust, and you
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can keep using those if they do what you need and you don't
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want to be on the bleeding edge. One site had a computer
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running version 0.97p1 (dating from the summer of
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1992) for over 136 days without an error or crash. (It would
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have been longer if the backhoe operator hadn't mistaken a main
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power transformer for a dumpster...) Others have posted uptimes
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in excess of a year. One site still had a computer running
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Linux 0.99p15s over 600 days at last report.
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<P>One thing to be aware of is that Linux is developed using an
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open and distributed model, instead of a closed and
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centralized model like much other software. This means that
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the current development version is always public (with up to a
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week or two of delay) so that anybody can use it. The result
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is that whenever a version with new functionality is released,
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it almost always contains bugs, but it also results in a very
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rapid development so that the bugs are found and corrected
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quickly, often in hours, as many people work to fix them.
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<P>In contrast, the closed and centralized model means that there is only
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one person or team working on the project, and they only release
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software that they think is working well. Often this leads to long
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intervals between releases, long waiting for bug fixes, and slower
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development. The latest release of such software to the
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public is sometimes of higher quality, but the development speed is
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generally much slower.
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<P>For a discussion of these two models, read ``The Cathedral and the Bazaar''
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at
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<A HREF="http://sagan.earthspace.net/~esr/writings/cathedral-bazaar/">http://sagan.earthspace.net/~esr/writings/cathedral-bazaar/</A>
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by Eric Raymond.
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<P>As of September 1, 1998, the current stable version of Linux is
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2.0.35, and the latest development version is 2.1.119.
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<P>
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