390 lines
11 KiB
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390 lines
11 KiB
HTML
<HTML
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>History of Unix, Linux, and Open Source / Free Software</TITLE
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>Secure Programming for Linux and Unix HOWTO</TH
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></TR
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WIDTH="10%"
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ALIGN="left"
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><A
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>Prev</A
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><TD
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WIDTH="80%"
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VALIGN="bottom"
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>Chapter 2. Background</TD
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WIDTH="10%"
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><H1
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><A
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NAME="HISTORY"
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></A
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>2.1. History of Unix, Linux, and Open Source / Free Software</H1
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="UNIX-HISTORY"
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></A
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>2.1.1. Unix</H2
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><P
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>In 1969-1970, Kenneth Thompson, Dennis Ritchie, and others at
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AT&T Bell Labs began developing
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a small operating system on a little-used PDP-7.
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The operating system was soon christened Unix, a pun on an earlier operating
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system project called MULTICS.
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In 1972-1973 the system was rewritten in the programming language C,
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an unusual step that was visionary: due to this decision, Unix was
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the first widely-used operating system that
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could switch from and outlive its original hardware.
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Other innovations were added to Unix as well, in part due to synergies
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between Bell Labs and the academic community.
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In 1979, the ``seventh edition'' (V7) version
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of Unix was released, the grandfather of all extant Unix systems.</P
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><P
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>After this point, the history of Unix becomes somewhat convoluted.
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The academic community, led by Berkeley, developed a variant called the
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Berkeley Software Distribution (BSD), while AT&T continued developing
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Unix under the names ``System III'' and later ``System V''.
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In the late 1980's through early 1990's
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the ``wars'' between these two major strains raged.
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After many years each variant adopted many of the key features of the other.
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Commercially, System V won the ``standards wars'' (getting most of its
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interfaces into the formal standards), and
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most hardware vendors switched to AT&T's System V.
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However, System V ended up incorporating many BSD innovations, so the
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resulting system was more a merger of the two branches.
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The BSD branch did not die, but instead became widely used
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for research, for PC hardware, and for
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single-purpose servers (e.g., many web sites use a BSD derivative).</P
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><P
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>The result was many different versions of Unix,
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all based on the original seventh edition.
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Most versions of Unix were proprietary and maintained by their respective
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hardware vendor, for example, Sun Solaris is a variant of System V.
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Three versions of the BSD branch of Unix ended up as open source:
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FreeBSD (concentrating on ease-of-installation for PC-type hardware),
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NetBSD (concentrating on many different CPU architectures), and
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a variant of NetBSD, OpenBSD (concentrating on security).
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More general information about Unix history can be found at
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<A
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HREF="http://www.datametrics.com/tech/unix/uxhistry/brf-hist.htm"
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TARGET="_top"
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>http://www.datametrics.com/tech/unix/uxhistry/brf-hist.htm</A
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>,
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<A
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HREF="http://perso.wanadoo.fr/levenez/unix"
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TARGET="_top"
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>http://perso.wanadoo.fr/levenez/unix</A
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>, and
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<A
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HREF="http://www.crackmonkey.org/unix.html"
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TARGET="_top"
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>http://www.crackmonkey.org/unix.html</A
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>.
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Much more information about the BSD history can be found in
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[McKusick 1999] and
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<A
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HREF="ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/src/share/misc/bsd-family-tree"
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TARGET="_top"
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>ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/src/share/misc/bsd-family-tree</A
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>.</P
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><P
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>A slightly old but interesting advocacy piece that presents arguments
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for using Unix-like systems (instead of Microsoft's products) is
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<A
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HREF="http://web.archive.org/web/20010801155417/www.unix-vs-nt.org/kirch"
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TARGET="_top"
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>John Kirch's paper ``Microsoft Windows NT Server 4.0 versus UNIX''</A
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>.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="FSF-HISTORY"
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></A
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>2.1.2. Free Software Foundation</H2
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><P
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>In 1984 Richard Stallman's Free Software Foundation (FSF) began the GNU
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project, a project to create a free version of the Unix operating system.
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By free, Stallman meant software that could be freely
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used, read, modified, and redistributed.
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The FSF successfully built a vast number of
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useful components, including a C compiler (gcc), an
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impressive text editor (emacs), and a host of fundamental tools.
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However, in the 1990's the FSF
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was having trouble developing the operating system kernel [FSF 1998];
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without a kernel their dream of a completely free operating system
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would not be realized.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="LINUX-HISTORY"
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></A
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>2.1.3. Linux</H2
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><P
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>In 1991 Linus Torvalds began developing an operating system kernel, which
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he named ``Linux'' [Torvalds 1999].
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This kernel could be combined with the FSF material and other components
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(in particular some of the BSD components and MIT's X-windows software) to
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produce a freely-modifiable and very useful operating system.
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This book will term the kernel itself the ``Linux kernel'' and
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an entire combination as ``Linux''.
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Note that many use the term ``GNU/Linux'' instead for this combination.</P
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><P
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>In the Linux community,
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different organizations have combined the available components differently.
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Each combination is called a ``distribution'', and the organizations that
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develop distributions are called ``distributors''.
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Common distributions include Red Hat, Mandrake, SuSE, Caldera, Corel,
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and Debian.
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There are differences between the various distributions,
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but all distributions are based on the same foundation: the
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Linux kernel and the GNU glibc libraries.
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Since both are covered by ``copyleft'' style licenses, changes to
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these foundations generally must be made available to all, a
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unifying force between the Linux distributions at their foundation
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that does not exist between the BSD and AT&T-derived Unix systems.
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This book is not specific to any Linux distribution; when it
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discusses Linux it presumes Linux
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kernel version 2.2 or greater and the C library glibc 2.1 or greater,
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valid assumptions for essentially all current major
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Linux distributions.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="OSS-HISTORY"
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></A
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>2.1.4. Open Source / Free Software</H2
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><P
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>Increased interest in software that is freely shared
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has made it increasingly necessary to define and explain it.
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A widely used term is ``open source software'', which is further defined in
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[OSI 1999].
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Eric Raymond [1997, 1998] wrote several seminal articles examining
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its various development processes.
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Another widely-used term is ``free software'', where the ``free''
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is short for ``freedom'': the usual explanation is ``free speech, not
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free beer.''
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Neither phrase is perfect.
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The term
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``free software'' is often confused with programs whose executables are
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given away at no charge, but whose source code cannot be viewed, modified,
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or redistributed.
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Conversely, the term ``open source'' is sometime (ab)used
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to mean software whose
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source code is visible, but for which there are limitations on
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use, modification, or redistribution.
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This book uses the term ``open source'' for its usual meaning, that
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is, software which has its source code freely available for
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use, viewing, modification, and redistribution; a more detailed
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definition is contained in the
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<A
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HREF="http://www.opensource.org/osd.html"
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TARGET="_top"
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>Open Source Definition</A
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>.
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In some cases, a difference in motive is suggested;
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those preferring the term ``free software'' wish to strongly
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emphasize the need for freedom, while those using the term may have
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other motives (e.g., higher reliability) or simply wish to appear less
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strident.
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For information on this definition of free software, and
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the motivations behind it, can be found at
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<A
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HREF="http://www.fsf.org"
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TARGET="_top"
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>http://www.fsf.org</A
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>.</P
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><P
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>Those interested in reading advocacy pieces for open source software
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and free software should see
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<A
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HREF="http://www.opensource.org"
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TARGET="_top"
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>http://www.opensource.org</A
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> and
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<A
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HREF="http://www.fsf.org"
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TARGET="_top"
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>http://www.fsf.org</A
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>.
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There are other documents which examine such software, for example,
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Miller [1995]
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found that the open source software were noticeably
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more reliable than proprietary software
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(using their measurement technique, which measured
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resistance to crashing due to random input).</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="LINUX-VS-UNIX"
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></A
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>2.1.5. Comparing Linux and Unix</H2
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><P
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>This book uses the term ``Unix-like'' to describe
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systems intentionally like Unix.
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In particular, the term ``Unix-like'' includes
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all major Unix variants and Linux distributions.
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Note that many people simply use the term ``Unix'' to describe these systems
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instead.
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Originally, the term ``Unix'' meant a particular product developed
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by AT&T.
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Today, the Open Group owns the Unix trademark, and it defines Unix as
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``the worldwide Single UNIX Specification''.</P
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><P
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>Linux is not derived from Unix source code, but its interfaces are
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intentionally like Unix.
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Therefore, Unix lessons learned generally apply to both, including information
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on security.
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Most of the information in this book applies to any Unix-like system.
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Linux-specific information has been intentionally added to
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enable those using Linux to take advantage of Linux's capabilities.</P
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><P
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>Unix-like systems share a number of security mechanisms, though there
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are subtle differences and not all systems have all mechanisms available.
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All include user and group ids (uids and gids) for each process and
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a filesystem with read, write, and execute permissions (for user, group, and
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other).
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See Thompson [1974] and Bach [1986]
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for general information on Unix systems, including their basic
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security mechanisms.
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<A
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HREF="features.html"
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>Chapter 3</A
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>
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summarizes key security features of Unix and Linux.</P
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></DIV
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