An operating system developed by AT&T Laboratories in the USA which has become widely adopted, particularly in educational centres, and is seen as a suitable operating system to form the basis of open systems interconnection. The Open Software Foundation is seeking to develop Unix as a standard operating system for this purpose.
Unix (officially trademarked as UNIX) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. Today's Unix systems are split into various branches, developed over time by AT&T, as well as various commercial vendors and non-profit organizations. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX" (others are called "Unix system-like" or "Unix-like").
During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption (particularly of the BSD variant, originating from the University of California, Berkeley) of Unix by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as Linux and Mac OS X are commonly encountered.
Sometimes, Traditional Unix may be used to describe a Unix or an operating system that has the characteristics of either Version 7 Unix or UNIX System V.
Overview
Unix operating systems are widely used in both servers and workstations. 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, causing both to be ported to a wider variety of machine families than any other operating system. As a result, Unix became synonymous with "open systems".
Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration. Unix systems are characterized by various concepts: the use of plain text for storing data;
Under Unix, the "operating system" consists of many of these utilities along with the master control program, the kernel.
History
In the 1960s, the Massachusetts Institute of Technology, AT&T Bell Labs, and General Electric worked on an experimental operating system called Multics (Multiplexed Information and Computing Service), which was designed to run on the GE-645 mainframe computer. Thompson and Ritchie led a team of developers, including Rudd Canaday, at Bell Labs developing a file system as well as the new multi-tasking operating system itself. The name has been attributed to Brian Kernighan, and was a play on Multics - Unix would do one thing, and do it well, rather than the overly general and bloated Multics system. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. For the first time in 1970, the UNIX Operating System was officially named and ran on the PDP-11/20. Bell Labs used this initial "text processing system", made up of Unix, roff, and the editor, for text processing of patent applications.
In 1973, the decision was made to re-write Unix in the C programming language. However, copies of the annotated Unix machine-dependent kernel circulated widely in the late 1970s in the form of a much-copied book by John Lions of the University of New South Wales, the Lions' Commentary on UNIX 6th Edition, with Source Code, which led to considerable adoption of Unix as an educational operating system.
Versions of the Unix system were determined by editions of its user manuals, so that (for example) "Fifth Edition UNIX" and "UNIX Version 5" have both been used to designate the same thing. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX, IS/1 (the first commercial Unix), and the University of Wollongong's port to the Interdata 7/32 (the first non-PDP Unix). Version 7 Unix, the last version of Research Unix to be released widely, was released in 1979.
1980s
AT&T now licensed UNIX System III, based largely on Version 7, for commercial use, the first version launching in 1982. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V Release 1. This introduced a few features such as the vi editor and curses from the Berkeley Software Distribution of Unix developed at the University of California, Berkeley.
Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD systems, notably the C shell with job control (modelled on ITS), Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP network code to the mainstream Unix kernel. The network code found in these releases is the ancestor of almost all TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and Microsoft Windows.
Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; In 1980, Microsoft announced its first Unix for 16-bit microcomputers called Xenix, which the Santa Cruz Operation (SCO) ported to the Intel 8086 processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.
In 1984, an industry group called X/Open was formed, with the aim of forming compatible open systems, that is, standardizing the UNIX environment. By the mid-1980s, the (largely gratuitous) incompatibilities between competing versions of Unix, popularly called "the Unix wars," were seen as hindering the adoption of Unix in a marketplace that was beginning to be dominated by Microsoft's operating systems. Inspired to some extent by the development of dual-mode (AT&T/BSD) versions of Unix, the IEEE Working Group P1003 developed the first POSIX standard for a Unix-based application programming interface, published in 1988.
AT&T added various features into UNIX System V, such as file locking, system administration, streams, the Remote File System and TLI. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open.
1990s
In 1990, the Open Software Foundation released OSF/1, their standard Unix implementation, based on Mach and BSD.
By 1993 most of the commercial vendors of UNIX had changed their commercial variants of Unix to be based on System V with many BSD features added on top. The creation of the COSE initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994.
Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX to Novell. (Dennis Ritchie likened this to the Biblical story of Esau selling his birthright for the proverbial "mess of pottage".) Novell developed its own version, UnixWare, merging its NetWare with UNIX System V Release 4.
In 1993, Novell decided to transfer the UNIX trademark and certification rights to the X/Open Consortium. Various standards by the Open Group now define what is and what is not a "UNIX" operating system, notably the post-1998 Single UNIX Specification.
In 1995, the business of administration and support of the existing UNIX licenses plus rights to further develop the System V code base were sold by Novell to the Santa Cruz Operation.
2000 to present
See also: SCO-Linux controversiesIn 2000, SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to The SCO Group. SCO have alleged that Linux contains copyrighted Unix code now owned by The SCO Group.
In 2005, Sun Microsystems released the bulk of its Solaris system code (based on UNIX System V Release 4) into an open source project called OpenSolaris.
The Dot-com crash has led to significant consolidation of UNIX users as well.
Standards
Beginning 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. At around the same time a separate but very similar standard, the Single UNIX Specification, was also produced by the Open Group.
In an effort towards compatibility, several Unix system vendors agreed on SVR4's Executable and Linkable Format (ELF) as standard for binary and object code files. The common format allows substantial binary compatibility among Unix systems operating on the same CPU architecture.
Components
The UNIX system is composed of several components that are normally packaged together. By including — in addition to the kernel of an operating system — the development environment, libraries, documents, and the portable, modifiable source-code for all of these components, UNIX was a self-contained software system.
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 10Mb, and arrived on a single 9-track magtape.
The names and filesystem locations of the Unix components has changed substantially across the history of the system. Nonetheless, the V7 implementation is considered by many to have the canonical early structure:
Kernel — originally found in /usr/sys, and composed of several sub-components: conf — originally found in /usr/sys/conf, and composed of configuration and machine-dependent parts, often including boot code dev — Device drivers (originally /usr/sys/dev) for control of hardware (and sometimes pseudo-hardware) sys — The "kernel" of the operating system, handling memory management, system calls, etc. h (or include) — Header files, generally defining key interfaces within the system, and important system-specific invariables Development Environment — Most implementations of Unix contained a development environment sufficient to recreate the system from source code. The development environment included: cc — The C language compiler (first appearing in V3 Unix) as — The machine-language assembler for the machine ld — The linker, for combining object files lib — Libraries. V7 Unix introduced the first version of the modern "Standard I/O" library stdio as part of the system library. make - The build manager (introduced in PWB/UNIX), designed to effectively automate the build process include — Header files for software development, defining standard interfaces and system invariants Other (secondary) languages — V7 Unix contained a Fortran-77 compiler, a programmable calculator, and the awk "scripting" language, and other versions and implementations have or now contain many other language compilers and toolsets. Early BSD releases included Pascal programming language tools, and many modern Unix systems also include the GNU Compiler Collection as well as or instead of a proprietary compiler system. Commands — Most Unix implementations make little distinction between commands (user-level programs) for system operation and maintenance (e.g. Nonetheless, some major categories are: sh — The Shell, the primary user-interface on Unix before window systems appeared, and the center of the command environment. Utilities — the core of the Unix command set, including ls, grep, find and many 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. 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 the first operating system to include all of its documentation online in machine-readable form. doc — Longer documents detailing major subsystems, such as the C language and troffImpact
The Unix system had a great impact on other operating systems. Unix has been called "the most important operating system you may never use."
It had a drastically simplified file model compared to many contemporary operating systems, treating all kinds of files as simple byte arrays.
Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. DEC's RSTS programmer/project hierarchy evolved into VMS directories, CP/M's volumes evolved into MS-DOS 2.0+ subdirectories, and HP's MPE group.account hierarchy and IBM's System 36 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 for example).
A fundamental simplifying assumption of Unix was its focus on ASCII text for nearly all of its 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 is the byte — unlike "record-based" file systems in other computers.
Unix popularised a syntax for regular expressions that found much wider use. The Unix programming interface became the basis for a standard operating system interface (POSIX, see above).
The C programming language, now ubiquitous in systems and applications programming, originated under Unix, and spread more quickly than Unix.
Early Unix developers were important in bringing the theory of modularity and reusability into software engineering practice.
Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the Internet explosion of world-wide real-time connectivity.
The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, contributing to the Open Source movement.
Over time, the leading developers of Unix (and programs that ran on it) developed a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself;
2038
Unix stores time values as the number of seconds from midnight January 1, 1970 (the "Unix Epoch") in variables of type time_t, historically defined as "signed 32-bit integer".
Since times before 1970 are rarely represented in Unix time, one possible solution that is compatible with existing binary formats would be to redefine time_t as "unsigned 32-bit integer".
Some Unix versions have already addressed this.
Free Unix-like operating systems
In 1983, Richard Stallman announced the GNU project, an ambitious effort to create a free software Unix-like system;
In addition to their use in the Linux 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.
A free derivative of BSD Unix, 386BSD, was also released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. BSDi), 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 directions, including the OpenBSD and DragonFly BSD variants.
Linux and the BSD kin are now rapidly occupying the market traditionally occupied by proprietary UNIX operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. A measure of this success may be seen when Apple Computer sought out a new foundation for its Macintosh operating system: it chose NEXTSTEP, an operating system developed by NeXT with a freely redistributable core operating system, renamed Darwin after Apple acquired it. The deployment of Darwin BSD Unix in Mac OS X makes it, according to a statement made by an Apple employee at a USENIX conference, the most widely-used Unix-based system in the desktop computer market. consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern BSDs also typically include some GNU utilities in their distribution, so Apple's combination of parts from NeXT and FreeBSD with Mach and some GNU utilities has precedent.
Branding
See also: list of Unix systemsIn 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. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX" (others are called "Unix system-like" or "Unix-like"). The term UNIX is not an acronym, but follows the early convention of naming computer systems in capital letters, such as ENIAC and MISTIC.
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 fee to The Open Group. Apple Computer have stated that they will be submitting Mac OS X 10.5 and Mac OS 10.5 Server to The Open Group for certification as a UNIX 03 system.
In practice, the term, especially when written as "Un*x", "*NIX", or "*N?X" is applied to a number of other multiuser POSIX-based systems such as GNU/Linux, Mac OS X and FreeBSD that do not seek UNIX branding because the royalties would be too expensive for a product marketed to consumers or freely available over the Internet; To avoid this, The Open Group requests that "UNIX" is always used as an adjective followed by a generic term such as "system".
The term "Unix" is also used, and in fact was the original capitalisation, but the name UNIX stuck because, in the words of Dennis Ritchie "when presenting the original Unix paper to the third Operating Systems Symposium of the American Association for Computing Machinery, we had just acquired a new typesetter and were intoxicated by being able to produce small caps" (quoted from the Jargon File, version 4.3.3, 20 September 2002).
Several plural forms of Unix are used to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional "Unixes", but the hacker culture which created Unix has a penchant for playful use of language, and "Unices" (treating Unix as Latin word) is also popular.
UNIX is also a trademarked name for a brand of carpet.
Common Unix commands
Wikibooks Guide to Unix has a page on the topic of Commands See also: list of Unix programsWidely used Unix commands include:
Directory and file creation and navigation: ls cd pwd mkdir rm rmdir cp find touch File viewing and editing: more less ed vi emacs head tail Text processing: echo cat grep sort uniq sed awk cut tr split printf File comparison: comm cmp diff patch Miscellaneous shell tools: yes test xargs System administration: chmod chown ps su w who Communication: mail telnet ftp finger ssh
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