articles/explaining-bsd/article.xml

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE article PUBLIC "-//FreeBSD//DTD DocBook XML V5.0-Based Extension//EN"
        "http://www.FreeBSD.org/XML/share/xml/freebsd50.dtd">
<!-- $FreeBSD$ -->
<!-- The FreeBSD Documentation Project -->
<article xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en">
  <info><title>Explaining BSD</title>
    

    <author><personname><firstname>Greg</firstname><surname>Lehey</surname></personname><affiliation>
        <address><email>grog@FreeBSD.org</email></address>
      </affiliation></author>

    <legalnotice xml:id="trademarks" role="trademarks">
      &tm-attrib.freebsd;
      &tm-attrib.amd;
      &tm-attrib.apple;
      &tm-attrib.intel;
      &tm-attrib.linux;
      &tm-attrib.opengroup;
      &tm-attrib.sparc;
      &tm-attrib.sun;
      &tm-attrib.unix;
      &tm-attrib.general;
    </legalnotice>

    <pubdate>$FreeBSD$</pubdate>

    <releaseinfo>$FreeBSD$</releaseinfo>

    <abstract>
      <para>In the open source world, the word <quote>Linux</quote> is almost
        synonymous with <quote>Operating System</quote>, but it is not the only
        open source &unix; operating system.</para>

      <para>So what is the secret?  Why is BSD not better known?  This white
        paper addresses these and other questions.</para>

      <para>Throughout this paper, differences between BSD and Linux will be
        noted <emphasis>like this</emphasis>.</para>
    </abstract>
  </info>

  <sect1 xml:id="what-is-bsd">
    <title>What is BSD?</title>

    <para>BSD stands for <quote>Berkeley Software Distribution</quote>.  It is
      the name of distributions of source code from the University of
      California, Berkeley, which were originally extensions to AT&amp;T's
      Research &unix; operating system.  Several open source operating system
      projects are based on a release of this source code known as
      4.4BSD-Lite.  In addition, they comprise a number of packages from other
      Open Source projects, including notably the GNU project.  The overall
      operating system comprises:</para>

    <itemizedlist>
      <listitem>
        <para>The BSD kernel, which handles process scheduling, memory
          management, symmetric multi-processing (SMP), device drivers,
          etc.</para>
      </listitem>

      <listitem>
        <para>The C library, the base API for the system.</para>

        <para><emphasis>The BSD C library is based on code from Berkeley, not
            the GNU project.</emphasis></para>
      </listitem>

      <listitem>
        <para>Utilities such as shells, file utilities, compilers and
          linkers.</para>

        <para><emphasis>Some of the utilities are derived from the GNU
            project, others are not.</emphasis></para>
      </listitem>

      <listitem>
        <para>The X Window system, which handles graphical display.</para>

        <para>The X Window system used in most versions of BSD is maintained
          by the
          <link xlink:href="http://www.X.org/">X.Org project</link>.
          &os; allows the user to choose from a variety of desktop
          environments, such as <application>Gnome</application>,
          <application>KDE</application>, or <application>Xfce</application>;
          and lightweight window managers like
          <application>Openbox</application>,
          <application>Fluxbox</application>, or
          <application>Awesome</application>.</para>
      </listitem>

      <listitem>
        <para>Many other programs and utilities.</para>
      </listitem>
    </itemizedlist>
  </sect1>

  <sect1 xml:id="what-a-real-unix">
    <title>What, a real &unix;?</title>

    <para>The BSD operating systems are not clones, but open source
      derivatives of AT&amp;T's Research &unix; operating system, which is also
      the ancestor of the modern &unix; System V.  This may surprise you.  How
      could that happen when AT&amp;T has never released its code as open
      source?</para>

    <para>It is true that AT&amp;T &unix; is not open source, and in a copyright
      sense BSD is very definitely <emphasis>not</emphasis> &unix;, but on the
      other hand, AT&amp;T has imported sources from other projects,
      noticeably the Computer Sciences Research Group (CSRG) of the University of
      California in Berkeley, CA.  Starting in 1976, the CSRG started
      releasing tapes of their software, calling them <emphasis>Berkeley
        Software Distribution</emphasis> or <emphasis>BSD</emphasis>.</para>

    <para>Initial BSD releases consisted mainly of user programs, but that
      changed dramatically when the CSRG landed a contract with the Defense
      Advanced Research Projects Agency (DARPA) to upgrade the communications
      protocols on their network, ARPANET.  The new protocols were known as
      the <emphasis>Internet Protocols</emphasis>, later
      <emphasis>TCP/IP</emphasis> after the most important protocols.  The
      first widely distributed implementation was part of 4.2BSD, in
      1982.</para>

    <para>In the course of the 1980s, a number of new workstation companies
      sprang up. Many preferred to license &unix; rather than developing
      operating systems for themselves.  In particular, Sun Microsystems
      licensed &unix; and implemented a version of 4.2BSD, which they called
      &sunos;.  When AT&amp;T themselves were allowed to sell &unix; commercially,
      they started with a somewhat bare-bones implementation called System
      III, to be quickly followed by System V.  The System V code base did not
      include networking, so all implementations included additional software
      from the BSD, including the TCP/IP software, but also utilities such as
      the <emphasis>csh</emphasis> shell and the <emphasis>vi</emphasis>
      editor.  Collectively, these enhancements were known as the
      <emphasis>Berkeley Extensions</emphasis>.</para>

    <para>The BSD tapes contained AT&amp;T source code and thus required a
      &unix; source license.  By 1990, the CSRG's funding was running out, and
      it faced closure. Some members of the group decided to release the BSD
      code, which was Open Source, without the AT&amp;T proprietary code.
      This finally happened with the <emphasis>Networking Tape 2</emphasis>,
      usually known as <emphasis>Net/2</emphasis>.  Net/2 was not a complete
      operating system: about 20% of the kernel code was missing.  One of the
      CSRG members, William F. Jolitz, wrote the remaining code and released
      it in early 1992 as <emphasis>386BSD</emphasis>.  At the same time,
      another group of ex-CSRG members formed a commercial company called
      <link xlink:href="http://www.bsdi.com/">Berkeley Software Design Inc.</link>
      and released a beta version of an operating system called
      <link xlink:href="http://www.bsdi.com/">BSD/386</link>, which was based on
      the same sources.  The name of the operating system was later changed
      to BSD/OS.</para>

    <para>386BSD never became a stable operating system.  Instead, two other
      projects split off from it in 1993:
      <link xlink:href="http://www.NetBSD.org/">NetBSD</link> and
      <link xlink:href="&url.base;/index.html">FreeBSD</link>.  The two projects
      originally diverged due to differences in patience waiting for
      improvements to 386BSD: the NetBSD people started early in the year,
      and the first version of FreeBSD was not ready until the end of the
      year.  In the meantime, the code base had diverged sufficiently to
      make it difficult to merge.  In addition, the projects had different
      aims, as we will see below.  In 1996,
      <link xlink:href="http://www.OpenBSD.org/">OpenBSD</link> split off from
        NetBSD, and in 2003,
      <link xlink:href="http://www.dragonflybsd.org/">DragonFlyBSD</link> split
        off from FreeBSD.</para>
  </sect1>

  <sect1 xml:id="why-is-bsd-not-better-known">
    <title>Why is BSD not better known?</title>

    <para>For a number of reasons, BSD is relatively unknown:</para>

    <orderedlist>
      <listitem>
        <para>The BSD developers are often more interested in polishing their
          code than marketing it.</para>
      </listitem>

      <listitem>
        <para>Much of Linux's popularity is due to factors external to the
          Linux projects, such as the press, and to companies formed to
          provide Linux services.  Until recently, the open source BSDs had no
          such proponents.</para>
      </listitem>

      <listitem>
        <para>BSD developers tend to be more experienced than Linux
          developers, and have less interest in making the system easy to use.
          Newcomers tend to feel more comfortable with Linux.</para>
      </listitem>

      <listitem>
        <para>In 1992, AT&amp;T sued
          <link xlink:href="http://www.bsdi.com/">BSDI</link>,
          the vendor of BSD/386, alleging that the product contained
          AT&amp;T-copyrighted code.  The case was settled out of court in
          1994, but the spectre of the litigation continues to haunt people.
          In March 2000 an article published on the web claimed
          that the court case had been <quote>recently settled</quote>.</para>

        <para>One detail that the lawsuit did clarify is the naming: in the
          1980s, BSD was known as <quote>BSD &unix;</quote>.  With the
          elimination of the last vestige of AT&amp;T code from BSD, it
          also lost the right to the name &unix;.  Thus you will see
          references in book titles to <quote>the 4.3BSD &unix; operating
            system</quote> and <quote>the 4.4BSD operating
            system</quote>.</para>
      </listitem>
    </orderedlist>
  </sect1>

  <sect1 xml:id="comparing-bsd-and-linux">
    <title>Comparing BSD and Linux</title>

    <para>So what is really the difference between, say, Debian Linux and
      FreeBSD?  For the average user, the difference is surprisingly small:
      Both are &unix; like operating systems.  Both are developed by
      non-commercial projects (this does not apply to many other Linux
      distributions, of course).  In the following section, we will look at BSD
      and compare it to Linux.  The description applies most closely to
      FreeBSD, which accounts for an estimated 80% of the BSD installations,
      but the differences from NetBSD, OpenBSD and DragonFlyBSD are small.
      </para>

    <sect2>
      <title>Who owns BSD?</title>

      <para>No one person or corporation owns BSD. It is created and
        distributed by a community of highly technical and committed
        contributors all over the world. Some of the components of BSD are
        Open Source projects in their own right and managed by different
        project maintainers.</para>
    </sect2>

    <sect2>
      <title>How is BSD developed and updated?</title>

      <para>The BSD kernels are developed and updated following the Open
        Source development model.  Each project maintains a publicly
        accessible <emphasis>source tree</emphasis>
        which contains all source files for the
        project, including documentation and other incidental files.
        Users can obtain a complete copy of any version.</para>

      <para>A large number of developers worldwide contribute to improvements
        to BSD.  They are divided into three kinds:</para>

      <itemizedlist>
        <listitem>
          <para><firstterm>Contributors</firstterm> write code or documentation.
            They are not permitted to commit (add code) directly to the source
            tree.  In order for their code to be included in the system, it
            must be reviewed and checked in by a registered developer, known
            as a <emphasis>committer</emphasis>.</para>
        </listitem>

        <listitem>
          <para><firstterm>Committers</firstterm> are developers with write
            access to the source tree.  In order to become a committer, an
            individual must show ability in the area in which they are
            active.</para>

          <para>
            It is at the individual committer's discretion whether they should
            obtain authority before committing changes to the source tree.  In
            general, an experienced committer may make changes which are
            obviously correct without obtaining consensus.  For example, a
            documentation project committer may correct typographical or
            grammatical errors without review.  On the other hand, developers
            making far-reaching or complicated changes are expected to submit
            their changes for review before committing them.  In extreme
            cases, a core team member with a function such as Principal
            Architect may order that changes be removed from the tree, a
            process known as <firstterm>backing out</firstterm>.  All committers
            receive mail describing each individual commit, so it is not
            possible to commit secretly.</para>
        </listitem>

        <listitem>
          <para>The <firstterm>Core team</firstterm>.  FreeBSD and
            NetBSD each have a core team which manages the project.  The
            core teams developed in the course of the projects, and their role
            is not always well-defined.  It is not necessary to be a developer
            in order to be a core team member, though it is normal.  The rules
            for the core team vary from one project to the other, but in
            general they have more say in the direction of the project than
            non-core team members have.</para>
        </listitem>
      </itemizedlist>

      <para>This arrangement differs from Linux in a number of ways:</para>

      <orderedlist>
        <listitem>
          <para>No one person controls the content of the system.  In
            practice, this difference is overrated, since the Principal Architect
            can require that code be backed out, and even in the Linux project
            several people are permitted to make changes.</para>
        </listitem>

        <listitem>
          <para>On the other hand, there <emphasis>is</emphasis> a central
            repository, a single place where you can find the entire operating
            system sources, including all older versions.</para>
        </listitem>

        <listitem>
          <para>BSD projects maintain the entire <quote>Operating
              System</quote>, not only the kernel. This distinction is only
            marginally useful: neither BSD nor Linux is useful without
            applications.  The applications used under BSD are frequently the
            same as the applications used under Linux.</para>
        </listitem>

        <listitem>
          <para>As a result of the formalized maintenance of a single SVN
            source tree, BSD development is clear, and it is possible to
            access any version of the system by release number or by date.
            SVN also allows incremental updates to the system: for example,
            the FreeBSD repository is updated about 100 times a day.  Most of
            these changes are small.</para>
        </listitem>
      </orderedlist>
    </sect2>

    <sect2>
      <title>BSD releases</title>

      <para>FreeBSD, NetBSD and OpenBSD provide the system in three different
        <quote>releases</quote>.  As with Linux, releases are assigned a
        number such as 1.4.1 or 3.5.  In addition, the version number has a
        suffix indicating its purpose:</para>

      <orderedlist>
        <listitem>
          <para>The development version of the system is called
            <firstterm>CURRENT</firstterm>.  FreeBSD assigns a number to
            CURRENT, for example FreeBSD 5.0-CURRENT.  NetBSD uses a slightly
            different naming scheme and appends a single-letter suffix which
            indicates changes in the internal interfaces, for example NetBSD
            1.4.3G.  OpenBSD does not assign a number (<quote>OpenBSD-current</quote>).
            All new development on the system goes into this branch.</para>
        </listitem>

        <listitem>
          <para>At regular intervals, between two and four times a year, the
            projects bring out a <firstterm>RELEASE</firstterm> version of the
            system, which is available on CD-ROM and for free download from
            FTP sites, for example OpenBSD 2.6-RELEASE or NetBSD 1.4-RELEASE.
            The RELEASE version is intended for end users and is the normal
            version of the system.  NetBSD also provides <emphasis>patch
              releases</emphasis> with a third digit, for example NetBSD
            1.4.2.</para>
        </listitem>

        <listitem>
          <para>As bugs are found in a RELEASE version, they are fixed, and
            the fixes are added to the SVN tree.  In FreeBSD, the resultant
            version is called the <firstterm>STABLE</firstterm> version, while in NetBSD and OpenBSD
            it continues to be called the RELEASE version.  Smaller new
            features can also be added to this branch after a period of test
            in the CURRENT branch.  Security and other important bug fixes
            are also applied to all supported RELEASE versions.</para>
        </listitem>
      </orderedlist>

      <para><emphasis>By contrast, Linux maintains two separate code trees:
          the stable version and the development version.  Stable versions
          have an even minor version number, such as 2.0, 2.2 or 2.4.
          Development versions have an odd minor version number, such as 2.1,
          2.3 or 2.5.  In each case, the number is followed by a further
          number designating the exact release.  In addition, each vendor adds
          their own userland programs and utilities, so the name of the
          distribution is also important.  Each distribution vendor also
          assigns version numbers to the distribution, so a complete
          description might be something like <quote>TurboLinux 6.0 with kernel
          2.2.14</quote></emphasis></para>
    </sect2>

    <sect2>
      <title>What versions of BSD are available?</title>

      <para>In contrast to the numerous Linux distributions, there are only
        four major open source BSDs.  Each BSD project maintains its own source
        tree and its own kernel.  In practice, though, there appear to be
        fewer divergences between the userland code of the projects than there
        is in Linux.</para>

      <para>It is difficult to categorize the goals of each project: the
        differences are very subjective.  Basically,</para>

      <itemizedlist>
        <listitem>
          <para>&os; aims for high performance and ease of use by
            end users, and is a favourite of web content providers.  It runs
            on a <link xlink:href="&url.base;/platforms/">number of platforms</link>
            and has significantly more users than the other projects.</para>
        </listitem>

        <listitem>
          <para>NetBSD aims for maximum portability: <quote>of course it runs
              NetBSD</quote>.  It runs on machines from palmtops to large
            servers, and has even been used on NASA space missions.  It is a
            particularly good choice for running on old non-&intel;
            hardware.</para>
        </listitem>

        <listitem>
          <para>OpenBSD aims for security and code purity: it uses a
            combination of the open source concept and rigorous code reviews
            to create a system which is demonstrably correct, making it the
            choice of security-conscious organizations such as banks, stock
            exchanges and US Government departments.  Like NetBSD, it runs on
            a number of platforms.</para>
        </listitem>

        <listitem>
          <para>DragonFlyBSD aims for high performance and scalability under
            everything from a single-node UP system to a massively clustered system.
            DragonFlyBSD has several long-range technical goals, but focus lies on
            providing a SMP-capable infrastructure that is easy to understand,
            maintain and develop for.</para>
        </listitem>
      </itemizedlist>

      <para>There are also two additional BSD &unix; operating systems which are not
        open source, BSD/OS and Apple's &macos; X:</para>

      <itemizedlist>
        <listitem>
          <para>BSD/OS was the oldest of the 4.4BSD derivatives.  It
            was not open source, though source code licenses were
            available at relatively low cost.  It resembled FreeBSD in
            many ways.  Two years after the acquisition of BSDi by
            Wind River Systems, BSD/OS failed to survive as an
            independent product.  Support and source code may still
            be available from Wind River, but all new development is
            focused on the VxWorks embedded operating system.</para>
        </listitem>

        <listitem>
          <para><link xlink:href="http://www.apple.com/macosx/server/">&macos;
              X</link> is the latest version of the operating system for
              &apple;'s
              &mac; line.  The BSD core of this operating
              system, <link xlink:href="http://developer.apple.com/darwin/">Darwin</link>,
              is available as a fully functional open source operating
              system for x86 and PPC computers.  The Aqua/Quartz
              graphics system and many other proprietary aspects of
              &macos; X remain closed-source, however.  Several Darwin
              developers are also FreeBSD committers, and
              vice-versa.</para>
        </listitem>
      </itemizedlist>
    </sect2>

    <sect2>
      <title>How does the BSD license differ from the GNU Public
        license?</title>

      <para>Linux is available under the
        <link xlink:href="http://www.fsf.org/copyleft/gpl.html">GNU General Public
          License</link> (GPL), which is designed to eliminate closed
        source software.  In particular, any derivative work of a product
        released under the GPL must also be supplied with source code if
        requested.  By contrast, the
        <link xlink:href="http://www.opensource.org/licenses/bsd-license.html">BSD
          license</link> is less restrictive: binary-only distributions are
          allowed.  This is particularly attractive for embedded
          applications.</para>
    </sect2>

    <sect2>
      <title>What else should I know?</title>

      <para>Since fewer applications are available for BSD than Linux, the BSD
        developers created a Linux compatibility package, which allows Linux
        programs to run under BSD.  The package includes both kernel
        modifications, in order to correctly perform Linux system calls, and
        Linux compatibility files such as the C library. There is no
        noticeable difference in execution speed between a Linux application
        running on a Linux machine and a Linux application running on a BSD
        machine of the same speed.</para>

      <para>The <quote>all from one supplier</quote> nature of BSD means that
        upgrades are much easier to handle than is frequently the case with
        Linux.  BSD handles library version upgrades by providing
        compatibility modules for earlier library versions, so it is possible
        to run binaries which are several years old with no problems.</para>
    </sect2>

    <sect2>
      <title>Which should I use, BSD or Linux?</title>

      <para>What does this all mean in practice?  Who should use BSD, who
        should use Linux?</para>

      <para>This is a very difficult question to answer.  Here are some
        guidelines:</para>

      <itemizedlist>
        <listitem>
          <para><quote>If it ain't broke, don't fix it</quote>: If you already
            use an open source operating system, and you are happy with it,
            there is probably no good reason to change.</para>
        </listitem>

        <listitem>
          <para>BSD systems, in particular FreeBSD, can have notably higher
            performance than Linux.  But this is not across the board.  In many
            cases, there is little or no difference in performance.  In some
            cases, Linux may perform better than FreeBSD.</para>
        </listitem>

        <listitem>
          <para>In general, BSD systems have a better reputation for
            reliability, mainly as a result of the more mature code
            base.</para>
        </listitem>

        <listitem>
          <para>BSD projects have a better reputation for the quality and
            completeness of their documentation. The various documentation
            projects aim to provide actively updated documentation, in many
            languages, and covering all aspects of the system.</para>
        </listitem>

        <listitem>
          <para>The BSD license may be more attractive than the GPL.</para>
        </listitem>

        <listitem>
          <para>BSD can execute most Linux binaries, while Linux can not execute BSD
            binaries.  Many BSD implementations can also execute binaries
            from other &unix; like systems.  As a result, BSD may present an
            easier migration route from other systems than
            Linux would.</para>
        </listitem>
      </itemizedlist>
    </sect2>

    <sect2>
      <title>Who provides support, service, and training for BSD?</title>

      <para>BSDi / <link xlink:href="http://www.freebsdmall.com">FreeBSD
        Mall, Inc.</link> have been providing support contracts for
        FreeBSD for nearly a decade.</para>

      <para>In addition, each of the projects has a list of consultants for
        hire:
        <link xlink:href="&url.base;/commercial/consult_bycat.html">FreeBSD</link>,
        <link xlink:href="http://www.netbsd.org/gallery/consultants.html">NetBSD</link>,
        and <link xlink:href="http://www.openbsd.org/support.html">OpenBSD</link>.</para>
    </sect2>
  </sect1>
</article>