======================================================================
= Unix =
======================================================================
Introduction
======================================================================
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user
computer operating systems that derive from the original AT&T
Unix, whose development started in 1969 at the Bell Labs research
center by Ken Thompson, Dennis Ritchie, and others. Initially intended
for use inside the Bell System, AT&T licensed Unix to outside
parties in the late 1970s, leading to a variety of both academic and
commercial Unix variants from vendors including University of
California, Berkeley (BSD), Microsoft (Xenix), Sun Microsystems
(SunOS/Solaris), HP/HPE (HP-UX), and IBM (AIX).
The early versions of Unix--which are retrospectively referred to as
"Research Unix"--ran on computers such as the PDP-11 and VAX; Unix was
commonly used on minicomputers and mainframes from the 1970s onwards.
It distinguished itself from its predecessors as the first portable
operating system: almost the entire operating system is written in the
C programming language (in 1973), which allows Unix to operate on
numerous platforms. Unix systems are characterized by a modular design
that is sometimes called the "Unix philosophy". According to this
philosophy, the operating system should provide a set of simple tools,
each of which performs a limited, well-defined function. A unified and
inode-based filesystem and an inter-process communication mechanism
known as "pipes" serve as the main means of communication, and a shell
scripting and command language (the Unix shell) is used to combine the
tools to perform complex workflows.
Version 7 in 1979 was the final widely released Research Unix, after
which AT&T sold UNIX System III, based on Version 7, commercially
in 1982; to avoid confusion between the Unix variants, AT&T
combined various versions developed by others and released it as UNIX
System V in 1983. However as these were closed-source, the University
of California, Berkeley continued developing BSD as an alternative.
Other vendors that were beginning to create commercialized versions of
Unix would base their version on either System V (like Silicon
Graphics's IRIX) or BSD (like SunOS). Amid the "Unix wars" of
standardization, AT&T alongside Sun merged System V, BSD, SunOS
and Xenix, soldifying their features into one package as UNIX System V
Release 4 (SVR4) in 1989, and it was commercialized by Unix System
Laboratories, an AT&T spinoff. A rival Unix by other vendors was
released as OSF/1, however most commercial Unix vendors eventually
changed their distributions to be based on SVR4 with BSD features
added on top.
AT&T sold Unix to Novell in 1992, who later sold the UNIX
trademark to a new industry consortium called The Open Group which
allow the use of the mark for certified operating systems that comply
with the Single UNIX Specification (SUS). Since the 1990s, Unix
systems have appeared on home-class computers: BSD/OS was the first to
be commercialized for i386 computers and since then free Unix-like
clones of existing systems have been developed, such as FreeBSD and
the combination of Linux and GNU, the latter of which have since
eclipsed Unix in popularity. Unix was, until 2005, the most widely
used server operating system. However in the present day, Unix
distributions like IBM AIX, Oracle Solaris and OpenServer continue to
be widely used in certain fields.
Overview
======================================================================
Unix was originally meant to be a convenient platform for programmers
developing software to be run on it and on other systems, rather than
for non-programmers. The system grew larger as the operating system
started spreading in academic circles, and as users added their own
tools to the system and shared them with colleagues.
At first, Unix was not designed to support multi-tasking or to be
portable. Later, Unix gradually gained multi-tasking and multi-user
capabilities in a time-sharing configuration, as well as portability.
Unix systems are characterized by various concepts: the use of plain
text for storing data; a hierarchical file system; treating devices
and certain types of inter-process communication (IPC) as files; and
the use of a large number of software tools, small programs that can
be strung together through a command-line interpreter using pipes, as
opposed to using a single monolithic program that includes all of the
same functionality. These concepts are collectively known as the "Unix
philosophy". Brian Kernighan and Rob Pike summarize this in 'The Unix
Programming Environment' as "the idea that the power of a system comes
more from the relationships among programs than from the programs
themselves".
By the early 1980s, users began seeing Unix as a potential universal
operating system, suitable for computers of all sizes. The Unix
environment and the client-server program model were essential
elements in the development of the Internet and the reshaping of
computing as centered in networks rather than in individual computers.
Both Unix and the C programming language were developed by AT&T
and distributed to government and academic institutions, which led to
both being ported to a wider variety of machine families than any
other operating system.
The Unix operating system consists of many libraries and utilities
along with the master control program, the kernel. The kernel provides
services to start and stop programs, handles the file system and other
common "low-level" tasks that most programs share, and schedules
access to avoid conflicts when programs try to access the same
resource or device simultaneously. To mediate such access, the kernel
has special rights, reflected in the distinction of 'kernel space'
from user space, the latter being a lower priority realm where most
application programs operate.
History
======================================================================
The origins of Unix date back to the mid-1960s when the Massachusetts
Institute of Technology, Bell Labs, and General Electric were
developing Multics, a time-sharing operating system for the GE 645
mainframe computer.
Multics featured several innovations, but also presented severe
problems. Frustrated by the size and complexity of Multics, but not by
its goals, individual researchers at Bell Labs started withdrawing
from the project. The last to leave were Ken Thompson, Dennis Ritchie,
Douglas McIlroy, and Joe Ossanna, who decided to reimplement their
experiences in a new project of smaller scale. This new operating
system was initially without organizational backing, and also without
a name.
The new operating system was a single-tasking system. In 1970, the
group coined the name 'Unics' for 'Uniplexed Information and Computing
Service' as a pun on 'Multics', which stood for 'Multiplexed
Information and Computer Services'. Brian Kernighan takes credit for
the idea, but adds that "no one can remember" the origin of the final
spelling 'Unix'. Dennis Ritchie, Doug McIlroy, and Peter G. Neumann
also credit Kernighan.
The operating system was originally written in assembly language, but
in 1973, Version 4 Unix was rewritten in C. Ken Thompson faced
multiple challenges attempting the kernel port due to the evolving
state of C, which lacked key features like structures at the time.
Version 4 Unix, however, still had much PDP-11 specific code, and was
not suitable for porting. The first port to another platform was a
port of Version 6, made four years later (1977) at the University of
Wollongong for the Interdata 7/32, followed by a Bell Labs port of
Version 7 to the Interdata 8/32 during 1977 and 1978.
Bell Labs produced several versions of Unix that are collectively
referred to as 'Research Unix'. In 1975, the first source license for
'UNIX' was sold to Donald B. Gillies at the University of Illinois
Urbana-Champaign (UIUC) Department of Computer Science.
During the late 1970s and early 1980s, the influence of Unix in
academic circles led to large-scale adoption of Unix (BSD and System
V) by commercial startups, which in turn led to Unix fragmenting into
multiple, similar -- but often slightly and mutually incompatible --
systems including DYNIX, HP-UX, SunOS/Solaris, AIX, and Xenix. In the
late 1980s, AT&T Unix System Laboratories and Sun Microsystems
developed System V Release 4 (SVR4), which was subsequently adopted by
many commercial Unix vendors.
In the 1990s, Unix and Unix-like systems grew in popularity and became
the operating system of choice for over 90% of the world's top 500
fastest supercomputers, as BSD and Linux distributions were developed
through collaboration by a worldwide network of programmers. In 2000,
Apple released Darwin, also a Unix system, which became the core of
the Mac OS X operating system, later renamed macOS.
Unix-like operating systems are widely used in modern servers,
workstations, and mobile devices.
Standards
======================================================================
In the late 1980s, an open operating system standardization effort now
known as POSIX provided a common baseline for all operating systems;
IEEE based POSIX around the common structure of the major competing
variants of the Unix system, publishing the first POSIX standard in
1988. In the early 1990s, a separate but very similar effort was
started by an industry consortium, the Common Open Software
Environment (COSE) initiative, which eventually became the Single UNIX
Specification (SUS) administered by The Open Group. Starting in 1998,
the Open Group and IEEE started the Austin Group, to provide a common
definition of POSIX and the Single UNIX Specification, which, by 2008,
had become the Open Group Base Specification.
In 1999, in an effort towards compatibility, several Unix system
vendors agreed on SVR4's Executable and Linkable Format (ELF) as the
standard for binary and object code files. The common format allows
substantial binary compatibility among different Unix systems
operating on the same CPU architecture.
The Filesystem Hierarchy Standard was created to provide a reference
directory layout for Unix-like operating systems; it has mainly been
used in Linux.
Components
======================================================================
The Unix system is composed of several components that were originally
packaged together. By including the development environment,
libraries, documents and the portable, modifiable source code for all
of these components, in addition to the kernel of an operating system,
Unix was a self-contained software system. This was one of the key
reasons it emerged as an important teaching and learning tool and has
had a broad influence. See , below.
The inclusion of these components did not make the system large the
original V7 UNIX distribution, consisting of copies of all of the
compiled binaries plus all of the source code and documentation
occupied less than 10 MB and arrived on a single nine-track magnetic
tape, earning its reputation as a portable system. The printed
documentation, typeset from the online sources, was contained in two
volumes.
The names and filesystem locations of the Unix components have changed
substantially across the history of the system. Nonetheless, the V7
implementation has the canonical early structure:
* 'Kernel' source code in /usr/sys, composed of several
sub-components:
** 'conf' configuration and machine-dependent parts, including boot
code
** 'dev' device drivers for control of hardware (and some
pseudo-hardware)
** 'sys' operating system "kernel", handling memory management,
process scheduling, system calls, etc.
** 'h' header files, defining key structures within the system and
important system-specific invariables
* 'Development environment' early versions of Unix contained a
development environment sufficient to recreate the entire system from
source code:
** 'ed' text editor, for creating source code files
** 'cc' C language compiler (first appeared in V3 Unix)
** 'as' machine-language assembler for the machine
** 'ld' linker, for combining object files
** 'lib' object-code libraries (installed in /lib or /usr/lib).
'libc', the system library with C run-time support, was the primary
library, but there have always been additional libraries for things
such as mathematical functions ('libm') or database access. V7 Unix
introduced the first version of the modern "Standard I/O" library
'stdio' as part of the system library. Later implementations increased
the number of libraries significantly.
** 'make' build manager (introduced in PWB/UNIX), for effectively
automating the build process
** 'include' header files for software development, defining standard
interfaces and system invariants
** 'Other languages' V7 Unix contained a Fortran-77 compiler, a
programmable arbitrary-precision calculator ('bc', 'dc'), and the awk
scripting language; later versions and implementations contain many
other language compilers and toolsets. Early BSD releases included
Pascal tools, and many modern Unix systems also include the GNU
Compiler Collection as well as or instead of a proprietary compiler
system.
** 'Other tools' including an object-code archive manager ('ar'),
symbol-table lister ('nm'), compiler-development tools (e.g. 'lex'
& 'yacc'), and debugging tools.
* 'Commands' Unix makes little distinction between commands
(user-level programs) for system operation and maintenance (e.g.
'cron'), commands of general utility (e.g. 'grep'), and more
general-purpose applications such as the text formatting and
typesetting package. Nonetheless, some major categories are:
** 'sh' the "shell" programmable command-line interpreter, the primary
user interface on Unix before window systems appeared, and even
afterward (within a "command window").
** 'Utilities' the core toolkit of the Unix command set, including
'cp', 'ls', 'grep', 'find' and many others. Subcategories include:
*** 'System utilities' administrative tools such as 'mkfs', 'fsck',
and many others.
*** 'User utilities' environment management tools such as 'passwd',
'kill', and others.
** 'Document formatting' Unix systems were used from the outset for
document preparation and typesetting systems, and included many
related programs such as 'nroff', 'troff', 'tbl', 'eqn', 'refer', and
'pic'. Some modern Unix systems also include packages such as TeX and
Ghostscript.
** 'Graphics' the 'plot' subsystem provided facilities for producing
simple vector plots in a device-independent format, with
device-specific interpreters to display such files. Modern Unix
systems also generally include X11 as a standard windowing system and
GUI, and many support OpenGL.
** 'Communications' early Unix systems contained no inter-system
communication, but did include the inter-user communication programs
'mail' and 'write'. V7 introduced the early inter-system communication
system UUCP, and systems beginning with BSD release 4.1c included
TCP/IP utilities.
* 'Documentation' Unix was one of the first operating systems to
include all of its documentation online in machine-readable form. The
documentation included:
** 'man' manual pages for each command, library component, system
call, header file, etc.
** 'doc' longer documents detailing major subsystems, such as the C
language and troff
Impact
======================================================================
The Unix system had a significant impact on other operating systems.
It achieved its reputation by its interactivity, by providing the
software at a nominal fee for educational use, by running on
inexpensive hardware, and by being easy to adapt and move to different
machines. Unix was originally written in assembly language, but was
soon rewritten in C, a high-level programming language. Although this
followed the lead of CTSS, Multics and Burroughs MCP, it was Unix that
popularized the idea.
Unix had a drastically simplified file model compared to many
contemporary operating systems: treating all kinds of files as simple
byte arrays. The file system hierarchy contained machine services and
devices (such as printers, terminals, or disk drives), providing a
uniform interface, but at the expense of occasionally requiring
additional mechanisms such as ioctl and mode flags to access features
of the hardware that did not fit the simple "stream of bytes" model.
The Plan 9 operating system pushed this model even further and
eliminated the need for additional mechanisms.
Unix also popularized the hierarchical file system with arbitrarily
nested subdirectories, originally introduced by Multics. Other common
operating systems of the era had ways to divide a storage device into
multiple directories or sections, but they had a fixed number of
levels, often only one level. Several major proprietary operating
systems eventually added recursive subdirectory capabilities also
patterned after Multics. DEC's RSX-11M's "group, user" hierarchy
evolved into OpenVMS directories, CP/M's volumes evolved into MS-DOS
2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's
SSP and OS/400 library systems were folded into broader POSIX file
systems.
Making the command interpreter an ordinary user-level program, with
additional commands provided as separate programs, was another Multics
innovation popularized by Unix. The Unix shell used the same language
for interactive commands as for scripting (shell scripts - there was
no separate job control language like IBM's JCL). Since the shell and
OS commands were "just another program", the user could choose (or
even write) their own shell. New commands could be added without
changing the shell itself. Unix's innovative command-line syntax for
creating modular chains of producer-consumer processes (pipelines)
made a powerful programming paradigm (coroutines) widely available.
Many later command-line interpreters have been inspired by the Unix
shell.
A fundamental simplifying assumption of Unix was its focus on
newline-delimited text for nearly all file formats. There were no
"binary" editors in the original version of Unix - the entire system
was configured using textual shell command scripts. The common
denominator in the I/O system was the byte - unlike "record-based"
file systems. The focus on text for representing nearly everything
made Unix pipes especially useful and encouraged the development of
simple, general tools that could easily be combined to perform more
complicated 'ad hoc' tasks. The focus on text and bytes made the
system far more scalable and portable than other systems. Over time,
text-based applications have also proven popular in application areas,
such as printing languages (PostScript, ODF), and at the application
layer of the Internet protocols, e.g., FTP, SMTP, HTTP, SOAP, and SIP.
Unix popularized a syntax for regular expressions that found
widespread use. The Unix programming interface became the basis for a
widely implemented operating system interface standard (POSIX, see
above). The C programming language soon spread beyond Unix, and is now
ubiquitous in systems and applications programming.
Early Unix developers were important in bringing the concepts of
modularity and reusability into software engineering practice,
spawning a "software tools" movement. Over time, the leading
developers of Unix (and programs that ran on it) established a set of
cultural norms for developing software, norms which became as
important and influential as the technology of Unix itself; this has
been termed the Unix philosophy.
The TCP/IP networking protocols were quickly implemented on the Unix
versions widely used on relatively inexpensive computers, which
contributed to the Internet explosion of worldwide, real-time
connectivity and formed the basis for implementations on many other
platforms.
The Unix policy of extensive on-line documentation and (for many
years) ready access to all system source code raised programmer
expectations, and contributed to the launch of the free software
movement in 1983.
Free Unix and Unix-like variants
==================================
In 1983, Richard Stallman announced the GNU (short for "GNU's Not
Unix") project, an ambitious effort to create a free software
Unix-like system--"free" in the sense that everyone who received a
copy would be free to use, study, modify, and redistribute it. The GNU
project's own kernel development project, GNU Hurd, had not yet
produced a working kernel, but in 1991 Linus Torvalds released the
Linux kernel as free software under the GNU General Public License. In
addition to their use in the GNU operating system, many GNU packages -
such as the GNU Compiler Collection (and the rest of the GNU
toolchain), the GNU C library and the GNU Core Utilities - have gone
on to play central roles in other free Unix systems as well.
Linux distributions, consisting of the Linux kernel and large
collections of compatible software have become popular both with
individual users and in business. Popular distributions include Red
Hat Enterprise Linux, Fedora, SUSE Linux Enterprise, openSUSE, Debian,
Ubuntu, Linux Mint, Slackware Linux, Arch Linux and Gentoo.
A free derivative of BSD Unix, 386BSD, was released in 1992 and led to
the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit
brought against the University of California and Berkeley Software
Design Inc. ('USL v. BSDi') by Unix System Laboratories, it was
clarified that Berkeley had the right to distribute BSD Unix for free
if it so desired. Since then, BSD Unix has been developed in several
different product branches, including OpenBSD and DragonFly BSD.
Because of the modular design of the Unix model, sharing components is
relatively common: most or all Unix and Unix-like systems include at
least some BSD code, while some include GNU utilities in their
distributions. Linux and BSD Unix are increasingly filling market
needs traditionally served by proprietary Unix operating systems,
expanding into new markets such as the consumer desktop, mobile
devices and embedded devices.
In a 1999 interview, Dennis Ritchie voiced his opinion that Linux and
BSD Unix operating systems are a continuation of the basis of the Unix
design and are derivatives of Unix:
In the same interview, he states that he views both Unix and Linux as
"the continuation of ideas that were started by Ken and me and many
others, many years ago".
OpenSolaris was the free software counterpart to Solaris developed by
Sun Microsystems, which included a CDDL-licensed kernel and a
primarily GNU userland. However, Oracle discontinued the project upon
their acquisition of Sun, which prompted a group of former Sun
employees and members of the OpenSolaris community to fork OpenSolaris
into the illumos kernel. As of 2014, illumos remains the only active,
open-source System V derivative.
ARPANET
=========
In May 1975, RFC 681 described the development of 'Network Unix' by
the Center for Advanced Computation at the University of Illinois
Urbana-Champaign. The Unix system was said to "present several
interesting capabilities as an ARPANET mini-host". At the time, Unix
required a license from Bell Telephone Laboratories that cost
US$20,000 for non-university institutions, while universities could
obtain a license for a nominal fee of $150. It was noted that Bell was
"open to suggestions" for an ARPANET-wide license.
The RFC specifically mentions that Unix "offers powerful local
processing facilities in terms of user programs, several compilers, an
editor based on QED, a versatile document preparation system, and an
efficient file system featuring sophisticated access control,
mountable and de-mountable volumes, and a unified treatment of
peripherals as special files." The latter permitted the Network
Control Program (NCP) to be integrated within the Unix file system,
treating network connections as special files that could be accessed
through standard Unix I/O calls, which included the added benefit of
closing all connections on program exit, should the user neglect to do
so. In order "to minimize the amount of code added to the basic Unix
kernel", much of the NCP code ran in a swappable user process, running
only when needed.
Branding
======================================================================
AT&T originally did not allow licensees to use the Unix name; thus
Microsoft called its variant Xenix, for example. In October 1988, they
allowed licensees to use the UNIX trademark for systems based on
System V Release 3.2, if certain conditions were met. In October 1993,
Novell, the company that owned the rights to the Unix System V source
at the time, transferred the trademarks of Unix to the X/Open Company
(now The Open Group), and in 1995 sold the related business operations
to Santa Cruz Operation (SCO). Whether Novell also sold the copyrights
to the actual software was the subject of a federal lawsuit in 2006,
'SCO v. Novell', which Novell won. The case was appealed, but on
August 30, 2011, the United States Court of Appeals for the Tenth
Circuit affirmed the trial decisions, closing the case. Unix vendor
SCO Group Inc. accused Novell of slander of title.
The present owner of the trademark 'UNIX' is The Open Group, an
industry standards consortium. Only systems fully compliant with and
certified to the Single UNIX Specification qualify as "UNIX" (others
are called "Unix-like").
By decree of The Open Group, the term "UNIX" refers more to a class of
operating systems than to a specific implementation of an operating
system; those operating systems which meet The Open Group's Single
UNIX Specification should be able to bear the UNIX 98 or UNIX 03
trademarks today, after the operating system's vendor pays a
substantial certification fee and annual trademark royalties to The
Open Group. Systems that have been licensed to use the UNIX trademark
include AIX, EulerOS, HP-UX, Inspur K-UX, IRIX, macOS, Solaris, Tru64
UNIX (formerly "Digital UNIX", or OSF/1), and z/OS. Notably, EulerOS
and Inspur K-UX are Linux distributions certified as UNIX 03
compliant.
Sometimes a representation like 'Un*x', '*NIX', or '*N?X' is used to
indicate all operating systems similar to Unix. This comes from the
use of the asterisk ('*') and the question mark characters as wildcard
indicators in many utilities. This notation is also used to describe
other Unix-like systems that have not met the requirements for UNIX
branding from the Open Group.
The Open Group requests that 'UNIX' always be used as an adjective
followed by a generic term such as 'system' to help avoid the creation
of a genericized trademark.
'Unix' was the original formatting, but the usage of 'UNIX' remains
widespread because it was once typeset in small caps ('Unix').
According to Dennis Ritchie, when presenting the original Unix paper
to the third Operating Systems Symposium of the American Association
for Computing Machinery (ACM), "we had a new typesetter and 'troff'
had just been invented and we were intoxicated by being able to
produce small caps". Many of the operating system's predecessors and
contemporaries used all-uppercase lettering, so many people wrote the
name in upper case due to force of habit. It is not an acronym.
Trademark names can be registered by different entities in different
countries and trademark laws in some countries allow the same
trademark name to be controlled by two different entities if each
entity uses the trademark in easily distinguishable categories. The
result is that Unix has been used as a brand name for various products
including bookshelves, ink pens, bottled glue, diapers, hair driers
and food containers.
Several plural forms of Unix are used casually to refer to multiple
brands of Unix and Unix-like systems. Most common is the conventional
'Unixes', but 'Unices', treating Unix as a Latin noun of the third
declension, is also popular. The pseudo-Anglo-Saxon plural form
'Unixen' is not common, although occasionally seen. Sun Microsystems,
developer of the Solaris variant, has asserted that the term 'Unix' is
itself plural, referencing its many implementations.
See also
======================================================================
* Comparison of operating systems and free and proprietary software
* List of operating systems, Unix systems, and Unix commands
* Plan 9 from Bell Labs
* Timeline of operating systems
* Unix time
* Market share of operating systems
* Year 2038 problem
Further reading
======================================================================
;General
*
*
*
*
* Lions, John: 'Lions' with Source Code', Peer-to-Peer
Communications, 1996;
;Books
* Salus, Peter H.: 'A Quarter Century of UNIX', Addison Wesley, June
1, 1994;
;Television
* Computer Chronicles (1985). "[
https://archive.org/details/UNIX1985
UNIX]".
* Computer Chronicles (1989). "[
https://archive.org/details/unix_2
Unix]".
;Talks
*
*
External links
======================================================================
* [
https://opengroup.org/unix The UNIX Standard], at The Open Group.
*
*
* [
https://www.tuhs.org/cgi-bin/utree.pl The Unix Tree: source code
and manuals from historic releases]
*
* [
https://www.bell-labs.com/usr/dmr/www/1stEdman.html The Unix 1st
Edition Manual]
** [
http://man.cat-v.org/unix-1st/ 1st Edition manual rendered to
HTML]
* (film about Unix featuring Dennis Ritchie, Ken Thompson, Brian
Kernighan, Alfred Aho, and more)
* (complementary film to the preceding "Making Computers More
Productive")
* [
https://archive.org/details/bsdtalk170 audio bsdtalk170 - Marshall
Kirk McKusick at DCBSDCon -- on history of tcp/ip (in BSD) --
abridgement of the three lectures on the history of BSD.]
* [
http://www.darwinsys.com/history/hist.html A History of UNIX before
Berkeley: UNIX Evolution: 1975-1984]
*
[
https://archive.org/stream/byte-magazine-1986-09/1986_09_BYTE_11-09_The_68000_Family#page/n171/mode/2up
BYTE Magazine, September 1986: UNIX and the MC68000] a software
perspective on the MC68000 CPU architecture and UNIX compatibility
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Unix
