Unix
thumb|300px|Filiation of Unix and Unix-like systemsUnix (officially trademarked as
UNIX, sometimes also written as
Unix with
small caps) is a computer
operating system originally developed in 1969 by a group of
AT&T employees at
Bell Labs, including
Ken Thompson,
Dennis Ritchie,
Douglas McIlroy, and
Joe Ossanna. 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. As of 2007, the owner of the
trademark is
The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the
Single UNIX Specification are qualified to use the trademark; others are called "Unix system-like" or "
Unix-like".During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix (particularly of the
BSD variant, originating from the
University of California, Berkeley) by commercial startups, the most notable of which are
Solaris,
HP-UX, and
AIX. Today, in addition to certified Unix systems,
Unix-like operating systems such as
Linux and
BSD 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
thumb|right|300px|Timeline of Unix variantsUnix 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; 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 known as the
Unix philosophy.Under Unix, the "operating system" consists of many of these utilities along with the master control program, the
kernel. The kernel provides services to start and stop programs, handle the
file system and other common "low level" tasks that most programs share, and, perhaps most importantly, schedules access to hardware to avoid conflicts if two programs try to access the same resource or device simultaneously. To mediate such access, the kernel was given special rights on the system, leading to the division between
user-space and
kernel-space.
The
microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a "normal" computer consisted of a hard disk for storage and a
data terminal for input and output (I/O), the Unix file model worked quite well as most I/O was "linear". However, modern systems include networking and other new devices. As graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a
mouse, and in the 1980s
non-blocking I/O and the set of
inter-process communication mechanisms was augmented (
sockets,
shared memory,
message queues,
semaphores), and functionalities such as network protocols were moved out of 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. (Eventually Multics became a commercial product, although sales did not meet expectations). Multics was an interactive operating system with many novel capabilities, including enhanced
security.AT&T Bell Labs pulled out of the Multics project and deployed its resources elsewhere. One of the developers on the Bell Labs team,
Ken Thompson, continued to develop for the GE-645 mainframe, and wrote a game for that computer called
Space Travel.
(1) However, he found that the game was too slow on the GE machine and was expensive, costing $75 per execution in scarce computing time.
(2)Thompson thus re-wrote the game in
assembly language for
Digital Equipment Corporation's
PDP-7 with help from
Dennis Ritchie. This experience, combined with his work on the Multics project, led Thompson to start a new operating system for the PDP-7. 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. They included a command line interpreter and some small utility programs.
(3) 1970s
In the 1970s the project was named
Unics, and eventually could support two simultaneous users.
Brian Kernighan invented this name as a contrast to
Multics; the spelling was later changed to
Unix.Up until this point there had been no financial support from Bell Labs. 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. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called
roff and a
text editor. All three were written in PDP-11/20 assembly language. Bell Labs used this initial "text processing system", made up of Unix, roff, and the editor, for text processing of
patent applications. Roff soon evolved into
troff, the first electronic publishing program with a full
typesetting capability. The
UNIX Programmer's Manual was published on
November 3 1971.In 1973, Unix was rewritten in the
C programming language, contrary to the general notion at the time "that something as complex as an operating system, which must deal with time-critical events, had to be written exclusively in assembly language".
(4) The migration from
assembly language to the
higher-level language C resulted in much more
portable software, requiring only a relatively small amount of machine-dependent code to be replaced when porting Unix to other
computing platforms.AT&T made Unix available to universities and commercial firms, as well as the
United States government under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources 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 use of Unix as an educational example.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. Development expanded, with Versions 4, 5, and
6 being released by 1975. These versions added the concept of pipes, leading to the development of a more modular code-base, increasing development speed still further. 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).In 1978,
UNIX/32V, for
DEC's then new
VAX system, was released. By this time, over 600 machines were running Unix in some form.
Version 7 Unix, the last version of
Research Unix to be released widely, was released in 1979. Versions
8,
9 and
10 were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of
Plan 9 from Bell Labs, a new portable distributed system.
1980s
AT&T licensed
UNIX System III, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. 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. This also included support for the
Western Electric 3B series of machines.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 releases, 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 BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe ("Tahoe" being the nickname of the
Computer Consoles Inc. Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the "Tahoe" naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of
Microsoft Windows. The accompanying
Berkeley sockets API is a de facto standard for networking APIs and has been copied on many platforms. 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; however, others were based on BSD instead. One of the leading developers of BSD,
Bill Joy, went on to co-found
Sun Microsystems in 1982 and created
SunOS (now
Solaris) for their
workstation computers. 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.For a few years during this period (before
PC compatible computers with
MS-DOS became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers.
(5) In 1984 several companies established the
X/Open consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the "
Unix wars," with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the
IEEE's
POSIX specification, designed as a compromise
API readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the
United States government for many of its own systemsAT&T added various features into UNIX System V, such as
file locking,
system administration,
STREAMS, new forms of
IPC, 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. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.During this time a number of vendors including Digital Equipment, Sun,
Addamax and others began building
trusted versions of UNIX for high security applications, mostly designed for military and law enforcement applications.
1990s
In 1990, the
Open Software Foundation released OSF/1, their standard Unix implementation, based on
Mach and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group "
UNIX International" in order to counteract OSF. This escalation of conflict between competing vendors gave rise again to the phrase "
Unix wars".In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (
BSDI). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of
386BSD, the free software ancestor of
FreeBSD,
OpenBSD, and
NetBSD.By 1993 most commercial vendors had changed their 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. The new combined entity, which retained the OSF name, stopped work on OSF/1 that year. By that time the only vendor using it was
Digital, which continued its own development, rebranding their product
Digital UNIX in early 1995.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".
(6)) Novell developed its own version,
UnixWare, merging its
NetWare with UNIX System V Release 4. Novell tried to use this to battle against
Windows NT, but their core markets suffered considerably.In 1993, Novell decided to transfer the UNIX®
trademark and certification rights to the
X/Open Consortium.
(7) In 1996, X/Open merged with
OSF, creating the
Open Group. 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 administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation.
(8) Whether Novell also sold the copyrights is currently the subject of litigation (see below).In 1997,
Apple Computer sought out a new foundation for its Macintosh operating system and chose
NEXTSTEP, an operating system developed by
NeXT. The core operating system, which was based on
BSD and the
Mach kernel, was renamed
Darwin after Apple acquired it. The deployment of Darwin 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.
2000 to present
In 2000,
SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to
The SCO Group.The
Dot-com crash (2001-2003) has led to significant consolidation of versions of Unix. Of the many commercial flavors of Unix that were born in the 1980s, only
Solaris,
HP-UX, and
AIX are still doing relatively well in the market, though SGI's
IRIX persisted for quite some time. Of these, Solaris has the largest market share.
(9)In 2003, the SCO Group started legal action against various users and vendors of Linux. SCO had alleged that Linux contained copyrighted Unix code now owned by The SCO Group. Other allegations included trade-secret violations by
IBM, or contract violations by former Santa Cruz customers who had since converted to Linux. However, Novell disputed the SCO Group's claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute resulted in the
SCO v. Novell lawsuit. On
August 10,
2007, a major portion of the case (the fact that Novell had the copyright to UNIX, and that the SCO Group had improperly kept money that was due to Novell) was decided in Novell's favor. The court also ruled that "SCO is obligated to recognize Novell's waiver of SCO's claims against IBM and Sequent". After the ruling, Novell announced they have no interest in suing people over Unix and stated, "We don't believe there is Unix in Linux".
(10)(11)(12){{seealso|SCO-Linux controversies}}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. New Sun OS technologies such as the
ZFS file system are now first released as open source code via the OpenSolaris project;
as of 2006 OpenSolaris has spawned several non-Sun distributions such as
SchilliX,
Belenix,
Nexenta, and MarTux.
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. 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 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.In an effort towards compatibility, in 1999 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 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, particularly Linux.
Components
{{seealso|List of Unix programs}}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. This was one of the key reasons it emerged as an important teaching and learning tool and has had such a broad influence.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 10MB, and arrived on a single 9-track
magnetic tape. The printed documentation, typeset from the on-line 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 is considered by many to have 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:
- 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 such things 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, and 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 tool kit 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.
missing image!
- man-man.png -
The 'man' command can display a manual page for every command on the system, including itself.
- Documentation — Unix was the first operating system 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
Unix impact
{{See also|Unix-like}}The Unix system had significant impact on other operating systems.It was written in high level language as opposed to
assembly language (which had been thought necessary for systems implementation on early computers). Although this followed the lead of
Multics and
Burroughs, 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
VMS 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) his own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating 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 ASCII 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 be easily 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), and at the application layer of the
Internet Protocols, e.g. Telnet, FTP, SSH, SMTP, HTTP 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 theory of
modularity and
reusability into
software engineering practice, spawning a "Software Tools" movement.Unix provided the TCP/IP networking protocol on relatively inexpensive computers, which contributed to the
Internet explosion of world-wide real-time connectivity, and which formed the basis for implementations on many other platforms. (This also exposed numerous security holes in the networking implementations.)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 1983 launch of the
free software movement.Over time, the leading developers of Unix (and programs that ran on it) evolved 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.
Free Unix-like operating systems
In 1983,
Richard Stallman announced the
GNU project, an ambitious effort to create a
free software Unix-like system; "free" in 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 produced a working kernel, but in 1992
Linus Torvalds released the
Linux kernel as free software under the
GNU General Public License. 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.Linux distributions, comprising Linux 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 GNU/Linux,
Ubuntu,
Mandriva Linux,
Slackware Linux and
Gentoo.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. (
USL v. 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
OpenBSD and
DragonFly BSD.Linux and BSD are now rapidly occupying much of 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. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern systems also usually include some GNU utilities in their distribution.In 2005,
Sun Microsystems released the bulk of the source code to the
Solaris operating system, a System V variant, under the name
OpenSolaris, making it the first actively developed commercial Unix system to be
open sourced (several years earlier, Caldera had released many of the older Unix systems under an educational and later
BSD license). As a result, a great deal of formerly proprietary AT&T/USL code is now freely available.
2038
Unix stores
system 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". On
January 19 2038, the current time will roll over from a zero followed by 31 ones (
01111111111111111111111111111111) to a one followed by 31 zeros (
10000000000000000000000000000000), which will reset time to the year 1901 or 1970, depending on implementation, because that toggles the
sign bit. As many applications use OS library routines for date calculations, the impact of this could be felt much earlier than 2038; for instance, 30-year mortages may be calculated incorrectly beginning in the year 2008.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". However, such a
kludge merely postpones the problem to
February 72106, and could introduce bugs in software that compares differences between two sets of time.Some Unix versions have already addressed this. For example, in Solaris on 64-bit systems,
time_t is 64 bits long, meaning that the OS itself and 64-bit applications will correctly handle dates for some 292 billion years. Existing 32-bit applications using a 32-bit
time_t continue to work on 64-bit Solaris systems but are still prone to the 2038 problem.
Branding
{{seealso|list of Unix systems}}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),
(13) and a part of
z/OS.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 "*" and "?" characters as "wildcard" characters in many utilities. This notation is also used to describe other Unix-like systems, e.g. Linux, BSD, etc., that have not met the requirements for UNIX® branding from the Open Group. The Open Group requests that "UNIX®" is always 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 "U
NIX" remains widespread because, according to
Dennis Ritchie, when presenting the original Unix paper to the third Operating Systems Symposium of the American
Association for Computing Machinery, “we had a new typesetter and troff had just been invented and we were intoxicated by being able to produce small caps.”
(14) 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.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 "
Unices" (treating Unix as
Latin noun of the
third declension) is also popular. The
Anglo-Saxon plural form "Unixen" is not common, although occasionally seen. 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 book shelves, ink pens, bottled glue, diapers, hair driers and food containers.
(15) Common Unix commands
{{seealso|List of Unix utilities}}Widely used Unix commands include:
- Directory and file creation and navigation:
ls cd pwd mkdir rm rmdir cp find touch mv
- 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
- Authentication:
su login passwd
References
-
[WEB, Dennis M., Ritchie, Space Travel: Exploring the solar system and the PDP-7,weblink 2007-03-11, ]
-
[The Creation of the UNIX* Operating System: The famous PDP-7 comes to the rescue]
-
[The Creation of the UNIX* Operating System: The UNIX system begins to take shape]
-
[Stallings, William. "Operating Systems: Internals and Design Principles" 5th ed, page 91. Pearson Education, Inc. 2005.]
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- weblink
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[weblink]
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[HP, Novell and SCO To Deliver High-Volume UNIX OS With Advanced Network And Enterprise Services]
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[Memorandum and Decision Order in SCO v. Novell]
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[Memorandum and Decision Order Civil Case No. 2:04CV139DAK]
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[Novell Won't Pursue Unix Copyrights August 15, 2007]
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[WEB, The Open Group, Mac OS X Version 10.5 Leopard on Intel-based Macintosh computers certification,weblink 2007-06-12, ]
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[Unix]
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[Autres Unix, autres moeurs (OtherUnix)]
- Ritchie, D.M.; Thompson, K., The UNIX Time-Sharing System (The Bell System Technical Journal, July-August 1978, Vol. 57, No. 6, Part 2)
- Salus, Peter H.: A Quarter Century of UNIX, Addison Wesley, June 1, 1994; ISBN 0-201-54777-5
- WEB,weblink UNIX History, www.levenez.com, 17 March, 2005,
- WEB,weblink AIX, FreeBSD, HP-UX, Linux, Solaris, Tru64, UNIXguide.net, 17 March, 2005,
- WEB,weblink Linux Weekly News, February 21, 2002, lwn.net, 7 April, 2006,
- Lions, John: Lions' WEB,weblink Commentary on the Sixth Edition UNIX Operating System, with Source Code, Peer-to-Peer Communications, 1996; ISBN 1-57398-013-7
- UNIX Shell Programming, Yashawant Kanetkar
External links
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