581 lines
25 KiB
XML
581 lines
25 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!DOCTYPE article PUBLIC "-//FreeBSD//DTD DocBook XML V5.0-Based Extension//EN"
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"http://www.FreeBSD.org/XML/share/xml/freebsd50.dtd">
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<!-- $FreeBSD$ -->
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<!-- The FreeBSD Documentation Project -->
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<article xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en">
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<info><title>Explaining BSD</title>
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<author><personname><firstname>Greg</firstname><surname>Lehey</surname></personname><affiliation>
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<address><email>grog@FreeBSD.org</email></address>
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</affiliation></author>
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<legalnotice xml:id="trademarks" role="trademarks">
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&tm-attrib.freebsd;
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&tm-attrib.amd;
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&tm-attrib.apple;
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&tm-attrib.intel;
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&tm-attrib.linux;
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&tm-attrib.opengroup;
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&tm-attrib.sparc;
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&tm-attrib.sun;
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&tm-attrib.unix;
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&tm-attrib.general;
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</legalnotice>
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<pubdate>$FreeBSD$</pubdate>
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<releaseinfo>$FreeBSD$</releaseinfo>
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<abstract>
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<para>In the open source world, the word <quote>Linux</quote> is almost
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synonymous with <quote>Operating System</quote>, but it is not the only
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open source &unix; operating system. According
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to the <link xlink:href="http://www.leb.net/hzo/ioscount/data/r.9904.txt">Internet
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Operating System Counter</link>, as of April 1999 31.3% of the
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world's network connected machines run Linux. 14.6% run BSD &unix;.
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Some of the world's largest web operations, such as <link xlink:href="http://www.yahoo.com/">Yahoo!</link>, run BSD. The world's
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busiest FTP server of 1999 (now defunct), <link xlink:href="ftp://ftp.cdrom.com/">ftp.cdrom.com</link>, used BSD to
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transfer 1.4 TB of data a day. Clearly this is not a niche
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market: BSD is a well-kept secret.</para>
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<para>So what is the secret? Why is BSD not better known? This white
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paper addresses these and other questions.</para>
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<para>Throughout this paper, differences between BSD and Linux will be
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noted <emphasis>like this</emphasis>.</para>
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</abstract>
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</info>
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<sect1 xml:id="what-is-bsd">
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<title>What is BSD?</title>
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<para>BSD stands for <quote>Berkeley Software Distribution</quote>. It is
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the name of distributions of source code from the University of
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California, Berkeley, which were originally extensions to AT&T's
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Research &unix; operating system. Several open source operating system
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projects are based on a release of this source code known as
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4.4BSD-Lite. In addition, they comprise a number of packages from other
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Open Source projects, including notably the GNU project. The overall
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operating system comprises:</para>
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<itemizedlist>
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<listitem>
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<para>The BSD kernel, which handles process scheduling, memory
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management, symmetric multi-processing (SMP), device drivers,
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etc.</para>
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<para><emphasis>Unlike the Linux kernel, there are several different
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BSD kernels with differing capabilities.</emphasis></para>
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</listitem>
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<listitem>
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<para>The C library, the base API for the system.</para>
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<para><emphasis>The BSD C library is based on code from Berkeley, not
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the GNU project.</emphasis></para>
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</listitem>
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<listitem>
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<para>Utilities such as shells, file utilities, compilers and
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linkers.</para>
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<para><emphasis>Some of the utilities are derived from the GNU
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project, others are not.</emphasis></para>
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</listitem>
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<listitem>
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<para>The X Window system, which handles graphical display.</para>
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<para>The X Window system used in most versions of BSD is maintained
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by the
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<link xlink:href="http://www.X.org/">X.Org project</link>.
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&os; allows the user to choose from a variety of desktop
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environments, such as <application>Gnome</application>,
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<application>KDE</application>, or <application>Xfce</application>;
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and lightweight window managers like
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<application>Openbox</application>,
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<application>Fluxbox</application>, or
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<application>Awesome</application>.</para>
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</listitem>
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<listitem>
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<para>Many other programs and utilities.</para>
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</listitem>
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</itemizedlist>
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</sect1>
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<sect1 xml:id="what-a-real-unix">
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<title>What, a real &unix;?</title>
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<para>The BSD operating systems are not clones, but open source
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derivatives of AT&T's Research &unix; operating system, which is also
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the ancestor of the modern &unix; System V. This may surprise you. How
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could that happen when AT&T has never released its code as open
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source?</para>
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<para>It is true that AT&T &unix; is not open source, and in a copyright
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sense BSD is very definitely <emphasis>not</emphasis> &unix;, but on the
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other hand, AT&T has imported sources from other projects,
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noticeably the Computer Sciences Research Group (CSRG) of the University of
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California in Berkeley, CA. Starting in 1976, the CSRG started
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releasing tapes of their software, calling them <emphasis>Berkeley
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Software Distribution</emphasis> or <emphasis>BSD</emphasis>.</para>
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<para>Initial BSD releases consisted mainly of user programs, but that
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changed dramatically when the CSRG landed a contract with the Defense
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Advanced Research Projects Agency (DARPA) to upgrade the communications
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protocols on their network, ARPANET. The new protocols were known as
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the <emphasis>Internet Protocols</emphasis>, later
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<emphasis>TCP/IP</emphasis> after the most important protocols. The
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first widely distributed implementation was part of 4.2BSD, in
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1982.</para>
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<para>In the course of the 1980s, a number of new workstation companies
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sprang up. Many preferred to license &unix; rather than developing
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operating systems for themselves. In particular, Sun Microsystems
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licensed &unix; and implemented a version of 4.2BSD, which they called
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&sunos;. When AT&T themselves were allowed to sell &unix; commercially,
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they started with a somewhat bare-bones implementation called System
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III, to be quickly followed by System V. The System V code base did not
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include networking, so all implementations included additional software
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from the BSD, including the TCP/IP software, but also utilities such as
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the <emphasis>csh</emphasis> shell and the <emphasis>vi</emphasis>
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editor. Collectively, these enhancements were known as the
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<emphasis>Berkeley Extensions</emphasis>.</para>
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<para>The BSD tapes contained AT&T source code and thus required a
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&unix; source license. By 1990, the CSRG's funding was running out, and
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it faced closure. Some members of the group decided to release the BSD
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code, which was Open Source, without the AT&T proprietary code.
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This finally happened with the <emphasis>Networking Tape 2</emphasis>,
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usually known as <emphasis>Net/2</emphasis>. Net/2 was not a complete
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operating system: about 20% of the kernel code was missing. One of the
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CSRG members, William F. Jolitz, wrote the remaining code and released
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it in early 1992 as <emphasis>386BSD</emphasis>. At the same time,
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another group of ex-CSRG members formed a commercial company called
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<link xlink:href="http://www.bsdi.com/">Berkeley Software Design Inc.</link>
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and released a beta version of an operating system called
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<link xlink:href="http://www.bsdi.com/">BSD/386</link>, which was based on
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the same sources. The name of the operating system was later changed
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to BSD/OS.</para>
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<para>386BSD never became a stable operating system. Instead, two other
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projects split off from it in 1993:
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<link xlink:href="http://www.NetBSD.org/">NetBSD</link> and
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<link xlink:href="&url.base;/index.html">FreeBSD</link>. The two projects
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originally diverged due to differences in patience waiting for
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improvements to 386BSD: the NetBSD people started early in the year,
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and the first version of FreeBSD was not ready until the end of the
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year. In the meantime, the code base had diverged sufficiently to
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make it difficult to merge. In addition, the projects had different
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aims, as we will see below. In 1996,
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<link xlink:href="http://www.OpenBSD.org/">OpenBSD</link> split off from
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NetBSD, and in 2003,
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<link xlink:href="http://www.dragonflybsd.org/">DragonFlyBSD</link> split
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off from FreeBSD.</para>
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</sect1>
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<sect1 xml:id="why-is-bsd-not-better-known">
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<title>Why is BSD not better known?</title>
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<para>For a number of reasons, BSD is relatively unknown:</para>
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<orderedlist>
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<listitem>
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<para>The BSD developers are often more interested in polishing their
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code than marketing it.</para>
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</listitem>
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<listitem>
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<para>Much of Linux's popularity is due to factors external to the
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Linux projects, such as the press, and to companies formed to
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provide Linux services. Until recently, the open source BSDs had no
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such proponents.</para>
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</listitem>
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<listitem>
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<para>BSD developers tend to be more experienced than Linux
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developers, and have less interest in making the system easy to use.
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Newcomers tend to feel more comfortable with Linux.</para>
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</listitem>
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<listitem>
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<para>In 1992, AT&T sued
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<link xlink:href="http://www.bsdi.com/">BSDI</link>,
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the vendor of BSD/386, alleging that the product contained
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AT&T-copyrighted code. The case was settled out of court in
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1994, but the spectre of the litigation continues to haunt people.
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As recently as March 2000 an article published on the web claimed
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that the court case had been <quote>recently settled</quote>.</para>
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<para>One detail that the lawsuit did clarify is the naming: in the
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1980s, BSD was known as <quote>BSD &unix;</quote>. With the
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elimination of the last vestige of AT&T code from BSD, it
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also lost the right to the name &unix;. Thus you will see
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references in book titles to <quote>the 4.3BSD &unix; operating
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system</quote> and <quote>the 4.4BSD operating
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system</quote>.</para>
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</listitem>
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<listitem>
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<para>There is a perception that the BSD projects are fragmented and
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belligerent. The
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<link xlink:href="http://interactive.wsj.com/bin/login?Tag=/&URI=/archive/retrieve.cgi%253Fid%253DSB952470579348918651.djm&">Wall Street
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Journal</link> spoke of <quote>balkanization</quote> of the
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BSD projects. Like the law suit, this perception bases mainly
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on ancient history.</para>
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</listitem>
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</orderedlist>
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</sect1>
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<sect1 xml:id="comparing-bsd-and-linux">
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<title>Comparing BSD and Linux</title>
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<para>So what is really the difference between, say, Debian Linux and
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FreeBSD? For the average user, the difference is surprisingly small:
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Both are &unix; like operating systems. Both are developed by
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non-commercial projects (this does not apply to many other Linux
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distributions, of course). In the following section, we will look at BSD
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and compare it to Linux. The description applies most closely to
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FreeBSD, which accounts for an estimated 80% of the BSD installations,
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but the differences from NetBSD, OpenBSD and DragonFlyBSD are small.
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</para>
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<sect2>
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<title>Who owns BSD?</title>
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<para>No one person or corporation owns BSD. It is created and
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distributed by a community of highly technical and committed
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contributors all over the world. Some of the components of BSD are
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Open Source projects in their own right and managed by different
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project maintainers.</para>
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</sect2>
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<sect2>
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<title>How is BSD developed and updated?</title>
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<para>The BSD kernels are developed and updated following the Open
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Source development model. Each project maintains a publicly
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accessible <emphasis>source tree</emphasis> under the
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<link xlink:href="http://www.cvshome.org/">Concurrent Versions
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System</link> (CVS), which contains all source files for the
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project, including documentation and other incidental files. CVS
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allows users to <quote>check out</quote> (in other words, to
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extract a copy of) any desired version of the system.</para>
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<para>A large number of developers worldwide contribute to improvements
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to BSD. They are divided into three kinds:</para>
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<itemizedlist>
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<listitem>
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<para><firstterm>Contributors</firstterm> write code or documentation.
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They are not permitted to commit (add code) directly to the source
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tree. In order for their code to be included in the system, it
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must be reviewed and checked in by a registered developer, known
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as a <emphasis>committer</emphasis>.</para>
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</listitem>
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<listitem>
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<para><firstterm>Committers</firstterm> are developers with write
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access to the source tree. In order to become a committer, an
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individual must show ability in the area in which he is
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active.</para>
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<para>
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It is at the individual committer's discretion whether he should
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obtain authority before committing changes to the source tree. In
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general, an experienced committer may make changes which are
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obviously correct without obtaining consensus. For example, a
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documentation project committer may correct typographical or
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grammatical errors without review. On the other hand, developers
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making far-reaching or complicated changes are expected to submit
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their changes for review before committing them. In extreme
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cases, a core team member with a function such as Principal
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Architect may order that changes be removed from the tree, a
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process known as <firstterm>backing out</firstterm>. All committers
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receive mail describing each individual commit, so it is not
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possible to commit secretly.</para>
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</listitem>
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<listitem>
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<para>The <firstterm>Core team</firstterm>. FreeBSD and
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NetBSD each have a core team which manages the project. The
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core teams developed in the course of the projects, and their role
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is not always well-defined. It is not necessary to be a developer
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in order to be a core team member, though it is normal. The rules
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for the core team vary from one project to the other, but in
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general they have more say in the direction of the project than
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non-core team members have.</para>
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</listitem>
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</itemizedlist>
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<para>This arrangement differs from Linux in a number of ways:</para>
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<orderedlist>
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<listitem>
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<para>No one person controls the content of the system. In
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practice, this difference is overrated, since the Principal Architect
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can require that code be backed out, and even in the Linux project
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several people are permitted to make changes.</para>
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</listitem>
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<listitem>
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<para>On the other hand, there <emphasis>is</emphasis> a central
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repository, a single place where you can find the entire operating
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system sources, including all older versions.</para>
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</listitem>
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<listitem>
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<para>BSD projects maintain the entire <quote>Operating
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System</quote>, not only the kernel. This distinction is only
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marginally useful: neither BSD nor Linux is useful without
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applications. The applications used under BSD are frequently the
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same as the applications used under Linux.</para>
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</listitem>
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<listitem>
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<para>As a result of the formalized maintenance of a single CVS
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source tree, BSD development is clear, and it is possible to
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access any version of the system by release number or by date.
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CVS also allows incremental updates to the system: for example,
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the FreeBSD repository is updated about 100 times a day. Most of
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these changes are small.</para>
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</listitem>
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</orderedlist>
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</sect2>
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<sect2>
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<title>BSD releases</title>
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<para>FreeBSD, NetBSD and OpenBSD provide the system in three different
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<quote>releases</quote>. As with Linux, releases are assigned a
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number such as 1.4.1 or 3.5. In addition, the version number has a
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suffix indicating its purpose:</para>
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<orderedlist>
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<listitem>
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<para>The development version of the system is called
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<firstterm>CURRENT</firstterm>. FreeBSD assigns a number to
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CURRENT, for example FreeBSD 5.0-CURRENT. NetBSD uses a slightly
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different naming scheme and appends a single-letter suffix which
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indicates changes in the internal interfaces, for example NetBSD
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1.4.3G. OpenBSD does not assign a number (<quote>OpenBSD-current</quote>).
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All new development on the system goes into this branch.</para>
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</listitem>
|
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|
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<listitem>
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<para>At regular intervals, between two and four times a year, the
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projects bring out a <firstterm>RELEASE</firstterm> version of the
|
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system, which is available on CD-ROM and for free download from
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FTP sites, for example OpenBSD 2.6-RELEASE or NetBSD 1.4-RELEASE.
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The RELEASE version is intended for end users and is the normal
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version of the system. NetBSD also provides <emphasis>patch
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releases</emphasis> with a third digit, for example NetBSD
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1.4.2.</para>
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</listitem>
|
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|
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<listitem>
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<para>As bugs are found in a RELEASE version, they are fixed, and
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the fixes are added to the CVS tree. In FreeBSD, the resultant
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version is called the <firstterm>STABLE</firstterm> version, while in NetBSD and OpenBSD
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|
it continues to be called the RELEASE version. Smaller new
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|
features can also be added to this branch after a period of test
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in the CURRENT branch.</para>
|
|
</listitem>
|
|
</orderedlist>
|
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|
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<para><emphasis>By contrast, Linux maintains two separate code trees:
|
|
the stable version and the development version. Stable versions
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|
have an even minor version number, such as 2.0, 2.2 or 2.4.
|
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Development versions have an odd minor version number, such as 2.1,
|
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2.3 or 2.5. In each case, the number is followed by a further
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number designating the exact release. In addition, each vendor adds
|
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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
|
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2.2.14</quote></emphasis></para>
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|
</sect2>
|
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|
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<sect2>
|
|
<title>What versions of BSD are available?</title>
|
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|
|
<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>FreeBSD aims for high performance and ease of use by
|
|
end users, and is a favourite of web content providers. It runs
|
|
on a number of platforms, including &i386; based systems (<quote>PCs</quote>),
|
|
systems based on the AMD 64-bit processors, &ultrasparc; based systems,
|
|
systems based on Compaq's Alpha processors and systems based around
|
|
the NEC PC-98 specification. The FreeBSD project 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>
|