9d68ff030b
- wrap long lines - put two spaces after a sentence stop - put <info> and <title> on lines on their own - in one instance, put the text right next to the <para> tag and not below it I did not change the capitalizations in this file, so the file should not have any visible changes.
601 lines
24 KiB
XML
601 lines
24 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"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
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xml:lang="en">
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<info>
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<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
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almost synonymous with <quote>Operating System</quote>, but it
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is not the only open source &unix; operating system.</para>
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<para>So what is the secret? Why is BSD not better known? This
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white paper addresses these and other questions.</para>
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<para>Throughout this paper, differences between BSD and Linux
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will be 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
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Distribution</quote>. It is the name of distributions of
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source code from the University of California, Berkeley, which
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were originally extensions to AT&T's Research &unix;
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operating system. Several open source operating system projects
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are based on a release of this source code known as 4.4BSD-Lite.
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In addition, they comprise a number of packages from other Open
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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
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drivers, etc.</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
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Berkeley, not 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
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display.</para>
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<para>The X Window system used in most versions of BSD is
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maintained by the <link xlink:href="http://www.X.org/">X.Org
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project</link>. &os; allows the user to choose from a
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variety of desktop environments, such as
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<application>Gnome</application>,
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<application>KDE</application>, or
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<application>Xfce</application>; and lightweight window
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managers like <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,
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which is also the ancestor of the modern &unix; System V. This
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may surprise you. How could that happen when AT&T has never
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released its code as open source?</para>
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<para>It is true that AT&T &unix; is not open source, and in a
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copyright sense BSD is very definitely <emphasis>not</emphasis>
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&unix;, but on the other hand, AT&T has imported sources
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from other projects, noticeably the Computer Sciences Research
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Group (CSRG) of the University of California in Berkeley, CA.
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Starting in 1976, the CSRG started releasing tapes of their
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software, calling them <emphasis>Berkeley Software
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Distribution</emphasis> or <emphasis>BSD</emphasis>.</para>
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<para>Initial BSD releases consisted mainly of user programs, but
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that changed dramatically when the CSRG landed a contract with
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the Defense Advanced Research Projects Agency (DARPA) to upgrade
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the communications protocols on their network, ARPANET. The new
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protocols were known as the <emphasis>Internet
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Protocols</emphasis>, later <emphasis>TCP/IP</emphasis> after
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the most important protocols. The first widely distributed
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implementation was part of 4.2BSD, in 1982.</para>
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<para>In the course of the 1980s, a number of new workstation
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companies sprang up. Many preferred to license &unix; rather
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than developing operating systems for themselves. In
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particular, Sun Microsystems licensed &unix; and implemented a
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version of 4.2BSD, which they called &sunos;. When AT&T
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themselves were allowed to sell &unix; commercially, they
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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
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did not include networking, so all implementations included
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additional software from the BSD, including the TCP/IP software,
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but also utilities such as the <emphasis>csh</emphasis> shell
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and the <emphasis>vi</emphasis> editor. Collectively, these
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enhancements were known as the <emphasis>Berkeley
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Extensions</emphasis>.</para>
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<para>The BSD tapes contained AT&T source code and thus
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required a &unix; source license. By 1990, the CSRG's funding
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was running out, and it faced closure. Some members of the
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group decided to release the BSD code, which was Open Source,
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without the AT&T proprietary code. This finally happened
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with the <emphasis>Networking Tape 2</emphasis>, usually known
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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
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of the CSRG members, William F. Jolitz, wrote the remaining code
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and released it in early 1992 as <emphasis>386BSD</emphasis>.
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At the same time, another group of ex-CSRG members formed a
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commercial company called <link
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xlink:href="http://www.bsdi.com/">Berkeley Software Design
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Inc.</link> and released a beta version of an operating system
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called <link xlink:href="http://www.bsdi.com/">BSD/386</link>,
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which was based on the same sources. The name of the operating
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system was later changed to BSD/OS.</para>
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<para>386BSD never became a stable operating system. Instead, two
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other projects split off from it in 1993: <link
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xlink:href="http://www.NetBSD.org/">NetBSD</link> and <link
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xlink:href="&url.base;/index.html">FreeBSD</link>. The two
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projects originally diverged due to differences in patience
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waiting for improvements to 386BSD: the NetBSD people started
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early in the year, and the first version of FreeBSD was not
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ready until the end of the year. In the meantime, the code base
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had diverged sufficiently to make it difficult to merge. In
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addition, the projects had different aims, as we will see below.
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In 1996, <link
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xlink:href="http://www.OpenBSD.org/">OpenBSD</link> split off
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from NetBSD, and in 2003, <link
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xlink:href="http://www.dragonflybsd.org/">DragonFlyBSD</link>
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split 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
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polishing their 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
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the Linux projects, such as the press, and to companies
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formed to provide Linux services. Until recently, the open
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source BSDs had no 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
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to use. Newcomers tend to feel more comfortable with
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Linux.</para>
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</listitem>
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<listitem>
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<para>In 1992, AT&T sued <link
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xlink:href="http://www.bsdi.com/">BSDI</link>, the vendor
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of BSD/386, alleging that the product contained
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AT&T-copyrighted code. The case was settled out of
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court in 1994, but the spectre of the litigation continues
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to haunt people. In March 2000 an article published on the
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web claimed that the court case had been <quote>recently
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settled</quote>.</para>
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<para>One detail that the lawsuit did clarify is the naming:
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in the 1980s, BSD was known as <quote>BSD &unix;</quote>.
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With the elimination of the last vestige of AT&T code
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from BSD, it also lost the right to the name &unix;. Thus
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you will see references in book titles to <quote>the 4.3BSD
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&unix; operating system</quote> and <quote>the 4.4BSD
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operating system</quote>.</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
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and FreeBSD? For the average user, the difference is
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surprisingly small: Both are &unix; like operating systems.
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Both are developed by non-commercial projects (this does not
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apply to many other Linux distributions, of course). In the
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following section, we will look at BSD and compare it to Linux.
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The description applies most closely to FreeBSD, which accounts
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for an estimated 80% of the BSD installations, but the
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differences from NetBSD, OpenBSD and DragonFlyBSD are
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small.</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
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BSD are Open Source projects in their own right and managed by
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different 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
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Open Source development model. Each project maintains a
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publicly accessible <emphasis>source tree</emphasis> which
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contains all source files for the project, including
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documentation and other incidental files. Users can obtain a
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complete copy of any version.</para>
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<para>A large number of developers worldwide contribute to
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improvements to BSD. They are divided into three
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kinds:</para>
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<itemizedlist>
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<listitem>
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<para><firstterm>Contributors</firstterm> write code or
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documentation. They are not permitted to commit (add
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code) directly to the source tree. In order for their
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code to be included in the system, it must be reviewed and
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checked in by a registered developer, known as a
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<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
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write access to the source tree. In order to become a
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committer, an individual must show ability in the area in
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which they are active.</para>
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<para>It is at the individual committer's discretion whether
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they should obtain authority before committing changes to
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the source tree. In general, an experienced committer may
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make changes which are obviously correct without obtaining
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consensus. For example, a documentation project committer
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may correct typographical or grammatical errors without
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review. On the other hand, developers making far-reaching
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or complicated changes are expected to submit their
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changes for review before committing them. In extreme
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cases, a core team member with a function such as
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Principal Architect may order that changes be removed from
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the tree, a process known as <firstterm>backing
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out</firstterm>. All committers receive mail describing
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each individual commit, so it is not possible to commit
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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.
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The core teams developed in the course of the projects,
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and their role is not always well-defined. It is not
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necessary to be a developer in order to be a core team
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member, though it is normal. The rules for the core team
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vary from one project to the other, but in general they
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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
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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
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Principal Architect can require that code be backed out,
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and even in the Linux project several people are permitted
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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
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central repository, a single place where you can find the
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entire operating system sources, including all older
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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
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is only marginally useful: neither BSD nor Linux is useful
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without applications. The applications used under BSD are
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frequently the same as the applications used under
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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
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SVN source tree, BSD development is clear, and it is
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possible to access any version of the system by release
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number or by date. SVN also allows incremental updates to
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the system: for example, the FreeBSD repository is updated
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about 100 times a day. Most of these changes are
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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
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different <quote>releases</quote>. As with Linux, releases
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are assigned a number such as 1.4.1 or 3.5. In addition, the
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version number has a 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
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to CURRENT, for example FreeBSD 5.0-CURRENT. NetBSD uses
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a slightly different naming scheme and appends a
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single-letter suffix which indicates changes in the
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internal interfaces, for example NetBSD 1.4.3G. OpenBSD
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does not assign a number (<quote>OpenBSD-current</quote>).
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All new development on the system goes into this
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branch.</para>
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</listitem>
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<listitem>
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<para>At regular intervals, between two and four times a
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year, the projects bring out a
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<firstterm>RELEASE</firstterm> version of the system,
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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
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1.4-RELEASE. The RELEASE version is intended for end
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users and is the normal version of the system. NetBSD
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also provides <emphasis>patch releases</emphasis> with a
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third digit, for example NetBSD 1.4.2.</para>
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</listitem>
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<listitem>
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<para>As bugs are found in a RELEASE version, they are
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fixed, and the fixes are added to the SVN tree. In
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FreeBSD, the resultant version is called the
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<firstterm>STABLE</firstterm> version, while in NetBSD and
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OpenBSD it continues to be called the RELEASE version.
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Smaller new features can also be added to this branch
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after a period of test in the CURRENT branch. Security
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and other important bug fixes are also applied to all
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supported RELEASE versions.</para>
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</listitem>
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</orderedlist>
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<para><emphasis>By contrast, Linux maintains two separate code
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trees: the stable version and the development version.
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Stable versions have an even minor version number, such as
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2.0, 2.2 or 2.4. Development versions have an odd minor
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version number, such as 2.1, 2.3 or 2.5. In each case, the
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number is followed by a further number designating the exact
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release. In addition, each vendor adds their own userland
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programs and utilities, so the name of the distribution is
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also important. Each distribution vendor also assigns
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version numbers to the distribution, so a complete
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description might be something like <quote>TurboLinux 6.0
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with kernel 2.2.14</quote></emphasis></para>
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</sect2>
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<sect2>
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<title>What versions of BSD are available?</title>
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<para>In contrast to the numerous Linux distributions, there are
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only four major open source BSDs. Each BSD project maintains
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its own source tree and its own kernel. In practice, though,
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there appear to be fewer divergences between the userland code
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of the projects than there is in Linux.</para>
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<para>It is difficult to categorize the goals of each project:
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the differences are very subjective. Basically,</para>
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<itemizedlist>
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<listitem>
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<para>&os; aims for high performance and ease of use by end
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users, and is a favourite of web content providers. It
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runs on a <link xlink:href="&url.base;/platforms/">number
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of platforms</link> and has significantly more users
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than the other projects.</para>
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</listitem>
|
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|
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<listitem>
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<para>NetBSD aims for maximum portability: <quote>of course
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it runs NetBSD</quote>. It runs on machines from
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palmtops to large servers, and has even been used on NASA
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space missions. It is a particularly good choice for
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running on old non-&intel; hardware.</para>
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</listitem>
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|
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<listitem>
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<para>OpenBSD aims for security and code purity: it uses a
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combination of the open source concept and rigorous code
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reviews to create a system which is demonstrably correct,
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making it the choice of security-conscious organizations
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such as banks, stock exchanges and US Government
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departments. Like NetBSD, it runs on a number of
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platforms.</para>
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</listitem>
|
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|
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<listitem>
|
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<para>DragonFlyBSD aims for high performance and scalability
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under everything from a single-node UP system to a
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massively clustered system. DragonFlyBSD has several
|
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long-range technical goals, but focus lies on providing a
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SMP-capable infrastructure that is easy to understand,
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maintain and develop for.</para>
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</listitem>
|
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</itemizedlist>
|
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|
|
<para>There are also two additional BSD &unix; operating systems
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which are not open source, BSD/OS and Apple's &macos;
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X:</para>
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|
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<itemizedlist>
|
|
<listitem>
|
|
<para>BSD/OS was the oldest of the 4.4BSD derivatives. It
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was not open source, though source code licenses were
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available at relatively low cost. It resembled FreeBSD in
|
|
many ways. Two years after the acquisition of BSDi by
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Wind River Systems, BSD/OS failed to survive as an
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|
independent product. Support and source code may still be
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available from Wind River, but all new development is
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focused on the VxWorks embedded operating system.</para>
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</listitem>
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<listitem>
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|
<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>
|