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A Unix-like
Unix-like
(sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix
Unix
system, while not necessarily conforming to or being certified to any version of the Single UNIX
UNIX
Specification. A Unix-like
Unix-like
application is one that behaves like the corresponding Unix
Unix
command or shell. There is no standard for defining the term, and some difference of opinion is possible as to the degree to which a given operating system or application is "Unix-like". The term can include free and open-source operating systems inspired by Bell Labs' Unix
Unix
or designed to emulate its features, commercial and proprietary work-alikes, and even versions based on the licensed UNIX source code (which may be sufficiently "Unix-like" to pass certification and bear the "UNIX" trademark).

Contents

1 Definition 2 History 3 Categories 4 Compatibility layers 5 See also 6 References 7 External links

Definition[edit] The Open Group owns the UNIX
UNIX
trademark and administers the Single UNIX Specification, with the "UNIX" name being used as a certification mark. They do not approve of the construction "Unix-like", and consider it a misuse of their trademark. Their guidelines require "UNIX" to be presented in uppercase or otherwise distinguished from the surrounding text, strongly encourage using it as a branding adjective for a generic word such as "system", and discourage its use in hyphenated phrases.[1] Other parties frequently treat "Unix" as a genericized trademark. Some add a wildcard character to the name to make an abbreviation like "Un*x"[2] or "*nix", since Unix-like
Unix-like
systems often have Unix-like names such as AIX, A/UX, HP-UX, IRIX, Linux, Minix, Ultrix, Xenix, Xinu, and XNU. These patterns do not literally match many system names, but are still generally recognized to refer to any UNIX descendant or work-alike system, even those with completely dissimilar names such as Darwin/macOS, illumos/Solaris or FreeBSD. In 2007, Wayne R. Gray sued to dispute the status of UNIX
UNIX
as a trademark, but lost his case, and lost again on appeal, with the court upholding the trademark and its ownership.[3][4] History[edit]

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Simplified history of Unix-like
Unix-like
operating systems.

"Unix-like" systems started to appear in the late 1970s and early 1980s. Many proprietary versions, such as Idris (1978), UNOS (1982), Coherent (1983), and UniFlex (1985), aimed to provide businesses with the functionality available to academic users of UNIX. When AT&T allowed relatively inexpensive commercial binary sub-licensing of UNIX
UNIX
in 1979, a variety of proprietary systems were developed based on it, including AIX, HP-UX, IRIX, SunOS, Tru64, Ultrix, and Xenix. These largely displaced the proprietary clones. Growing incompatibility among these systems led to the creation of interoperability standards, including POSIX and the Single UNIX Specification. Various free, low-cost, and unrestricted substitutes for UNIX
UNIX
emerged in the 1980s and 1990s, including 4.4BSD, Linux, and Minix. Some of these have in turn been the basis for commercial "Unix-like" systems, such as BSD/OS and macOS. Several versions of (Mac) OS X/macOS running on Intel-based Mac computers have been certified under the Single UNIX Specification.[5][6][7][8][9][10][11] The BSD variants are descendants of UNIX
UNIX
developed by the University of California at Berkeley with UNIX
UNIX
source code from Bell Labs. However, the BSD code base has evolved since then, replacing all of the AT&T code. Since the BSD variants are not certified as compliant with the Single UNIX Specification, they are referred to as "UNIX-like" rather than "UNIX". Categories[edit] Dennis Ritchie, one of the original creators of Unix, expressed his opinion that Unix-like
Unix-like
systems such as Linux
Linux
are de facto Unix systems.[12] Eric S. Raymond
Eric S. Raymond
and Rob Landley have suggested that there are three kinds of Unix-like
Unix-like
systems:[13]

Genetic UNIX Those systems with a historical connection to the AT&T codebase. Most (but not all) commercial UNIX
UNIX
systems fall into this category. So do the BSD systems, which are descendants of work done at the University of California, Berkeley
University of California, Berkeley
in the late 1970s and early 1980s. Some of these systems have no original AT&T code but can still trace their ancestry to AT&T designs.

Trademark
Trademark
or branded UNIX These systems‍—‌largely commercial in nature‍—‌have been determined by the Open Group to meet the Single UNIX Specification and are allowed to carry the UNIX
UNIX
name. Most such systems are commercial derivatives of the System V
System V
code base in one form or another, although Apple macOS 10.5 and later is a BSD variant that has been certified, and a few other systems (such as IBM z/OS) earned the trademark through a POSIX compatibility layer and are not otherwise inherently Unix
Unix
systems. Many ancient UNIX
UNIX
systems no longer meet this definition.

Functional UNIX Broadly, any Unix-like
Unix-like
system that behaves in a manner roughly consistent with the UNIX
UNIX
specification, including having a "program which manages your login and command line sessions";[14] more specifically, this can refer to systems such as Linux
Linux
or Minix
Minix
that behave similarly to a UNIX
UNIX
system but have no genetic or trademark connection to the AT&T code base. Most free/open-source implementations of the UNIX
UNIX
design, whether genetic UNIX
UNIX
or not, fall into the restricted definition of this third category due to the expense of obtaining Open Group certification, which costs thousands of dollars[citation needed] for commercial closed source systems. Around 2001, Linux
Linux
was given the opportunity to get a certification including free help from the POSIX chair Andrew Josey for the symbolic price of one dollar.[citation needed] There have been some activities to make Linux
Linux
POSIX-compliant, with Josey having prepared a list of differences between the POSIX standard and the Linux
Linux
Standard Base specification,[15] but in August 2005, this project was shut down because of missing interest at the LSB work group.[citation needed]

Compatibility layers[edit] Some non- Unix-like
Unix-like
operating systems provide a Unix-like
Unix-like
compatibility layer, with variable degrees of Unix-like
Unix-like
functionality.

IBM z/OS's UNIX
UNIX
System Services is sufficiently complete to be certified as trademark UNIX. Cygwin
Cygwin
and MSYS both provide a GNU
GNU
environment on top of the Microsoft Windows user API, sufficient for most common open source software to be compiled and run. The MKS Toolkit and UWIN are comprehensive interoperability tools which allow the porting of Unix
Unix
programmes to Windows. Windows NT
Windows NT
type systems have a Posix environmental subsystem Subsystem for Unix-based Applications (previously Interix) provides Unix-like
Unix-like
functionality as a Windows NT
Windows NT
subsystem (discontinued). Windows Subsystem for Linux
Linux
provides a Linux-compatible kernel interface developed by Microsoft and containing no Linux
Linux
code, with Ubuntu user-mode binaries running on top of it.[16]

Other means of Windows- Unix
Unix
interoperability include:

The above Windows packages can be used with various X servers for Windows Hummingbird Connectivity provides several ways for Windows machines to connect to Unix
Unix
and Linux
Linux
machines, from terminal emulators to X clients and servers, and others The Windows Resource Kits for versions of Windows NT
Windows NT
include a Bourne Shell, some command-line tools, and a version of Perl The Hamilton C Shell
Hamilton C Shell
is a version of csh written specifically for Windows.

See also[edit]

Information technology portal

Berkeley Software Distribution Linux
Linux
distribution List of Linux
Linux
distributions List of Unix
Unix
utilities List of operating systems

References[edit]

^ "Legal: Trademark
Trademark
Guidelines". The Open Group. Archived from the original on October 2, 2013. Retrieved November 4, 2013.  ^ Eric S. Raymond; Guy L. Steele Jr.
Guy L. Steele Jr.
"UN*X". The Jargon File. Retrieved January 22, 2009.  ^ Gray v. Novell, X/Open Company, The SCO Group (11th Cir. January 7, 2011). Text ^ "More Wayne Gray. No! Again? Still?! Yes. He Wants to Reopen Discovery in the USPTO Dispute". Groklaw. April 22, 2011. Retrieved February 5, 2013.  ^ "Mac OS X Version 10.5 on Intel-based Macintosh computers". The Open Group. Retrieved December 4, 2014.  ^ "Mac OS X Version 10.6 on Intel-based Macintosh computers". The Open Group. Retrieved December 4, 2014.  ^ "Mac OS X Version 10.8 on Intel-based Macintosh computers". The Open Group. Retrieved December 4, 2014.  ^ "OS X Version 10.9 on Intel-based Macintosh computers". The Open Group. Retrieved December 4, 2014.  ^ "OS X version 10.10 Yosemite on Intel-based Mac computers". The Open Group. Retrieved October 23, 2015.  ^ "OS X version 10.11 El Capitan on Intel-based Mac computers". The Open Group. Retrieved October 23, 2015.  ^ "macOS version 10.12 Sierra on Intel-based Mac computers". The Open Group. Retrieved October 13, 2016.  ^ Interview with Dennis M. Ritchie Manuel Benet, LinuxFocus, July 1999 ^ The meaning of 'Unix' Eric Raymond and Rob Landley, OSI Position Paper on the SCO-vs.-IBM Complaint ^ "Introduction to UNIX
UNIX
- Part 1: Basic Concepts". Retrieved April 4, 2014.  ^ Andrew Josey (August 20, 2005). "Conflicts between ISO/IEC 9945 (POSIX) and the Linux
Linux
Standard Base". The Open Group. Retrieved July 23, 2012.  ^ BASH Running in Ubuntu on Windows - MSDN

External links[edit]

Unix-like
Unix-like
Definition, by The Linux
Linux
Information Project (LINFO) UNIX
UNIX
history – a history time line graph of most UNIX
UNIX
and Unix-like
Unix-like
systems by Éric Lévénez Grokline's UNIX
UNIX
Ownership History Project – a project to map out the technical history of UNIX
UNIX
and Unix-like
Unix-like
systems at the Wayback Machine (archived June 22, 2004)

v t e

Unix
Unix
and Unix-like
Unix-like
operating systems

BSD

386BSD

FreeBSD NetBSD OpenBSD DragonFly BSD

NeXTSTEP Darwin

macOS iOS watchOS tvOS audioOS

SunOS Ultrix

Coherent GNU Linux

Android Chrome OS

LynxOS MINIX QNX

BlackBerry 10

Research Unix System V

A/UX AIX HP-UX illumos IRIX OpenServer Solaris Tru64 UNIX UnixWare

Xenix more...

Italics indicate discontinued branches. Category Commons Book

v t e

Unix
Unix
shells

Bash Bourne Almquist csh es fish Hamilton Korn PWB rc sash tcsh Thompson Wish Zsh

v t e

Unix
Unix
command-line interface programs and shell builtins

File
File
system

cat chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask

Processes

at bg crontab fg kill nice ps time

User environment

env exit logname mesg talk tput uname who write

Text processing

awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste printf sed sort strings tail tr uniq vi wc xargs

Shell builtins

alias cd echo test unset wait

Searching

find grep

Documentation

man

Software development

ar ctags lex make nm strip yacc

Miscellaneous

bc cal expr lp od sleep true and false

Categories

Standard Unix
Unix
programs Unix
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List

v t e

Operating systems

General

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Kernel

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Components

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Process management

Concepts

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Scheduling algorithms

Computer multitasking Fixed-priority preemptive Multilevel feedback queue Preemptive Round-robin Shortest job next

Memory management
Memory management
and resource protection

Bus error General protection fault Memory protection Paging Protection ring Segmentation fault Virtual memory

Storage access and file systems

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List

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Miscellaneous concepts

API Computer network HAL Live CD Live USB OS shell

CLI GUI

.