Derivado desta pergunta :
Se o opensolaris, freebsd, openbsd, netbsd não forem UNIX, o que é então?
O que mais me confunde é o fato de o OSX1.5 + ser UNIX, enquanto a versão anterior do OSX não era
Qual é a diferença entre o UNIX e o UNIX?
E qual é a diferença entre UNIX-Like e Linux?
UNIX é Unix e Unix é unix. Mas o unix pode não ser Unix e o Unix nem sempre é UNIX .
Wikipedia no Unix :
Unix (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, Brian Kernighan, Douglas McIlroy, and Joe Ossanna. Today the term Unix is used to describe any operating system that conforms to Unix standards, meaning the core operating system operates the same as the original Unix operating system. 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 according to the Single UNIX Specification are qualified to use the trademark; others are called "Unix system-like" or "Unix-like".
.. em semelhante ao Unix :
*A Unix-like (sometimes shortened to nix to circumvent trademark issues) operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification.
There is no standard for defining the term, and some difference of opinion is possible as to whether or not a certain OS is "Unix-like".
.. em Linux :
A Linux-based system is a modular Unix-like operating system. It derives much of its basic design from principles established in Unix during the 1970s and 1980s. Such a system uses a monolithic kernel, the Linux kernel, which handles process control, networking, and peripheral and file system access. [...]
Separate projects that interface with the kernel provide much of the system's higher-level functionality. The GNU userland is an important part of most Linux-based systems, [...]
.. em BSD (FreeBSD, NetBSD, OpenBSD) :
Berkeley Software Distribution (BSD, sometimes called Berkeley Unix) is the UNIX operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995.
Historically, BSD has been considered a branch of UNIX — "BSD UNIX", because it shared the initial codebase and design with the original AT&T UNIX operating system. In the 1980s, BSD was widely adopted by vendors of workstation-class systems in the form of proprietary UNIX variants such as DEC ULTRIX and Sun Microsystems SunOS. This can be attributed to the ease with which it could be licensed, and the familiarity it found among the founders of many technology companies of this era. [...]
Today, the term of "BSD" is often non-specifically used to refer to any of these BSD descendants, e.g. FreeBSD, NetBSD or OpenBSD, which together form a branch of the family of Unix-like operating systems.
.. e em OS X 10.5 :
Mac OS X v10.5 "Leopard" was released on October 26, 2007. It was called by Apple "the largest update of Mac OS X". [...] Leopard is an Open Brand UNIX 03 registered product on the Intel platform. It is also the first BSD-based OS to receive UNIX 03 certification.
Unix é uma marca comercial de propriedade do The Open Group. "Somente sistemas totalmente compatíveis e certificados de acordo com a Especificação Single UNIX estão qualificados para usar a marca registrada." (1) ( 2)
Isso explica por que a versão do OSX anterior a 1.5 não é UNIX, porque não era totalmente compatível.
OS X, Solaris, HP-UX e AIX são as distribuições UNIX restantes que estão indo bem no mercado. UNIX-Like refere-se a um sistema operacional que se comporta como o UNIX tradicional (métodos de bifurcação, o mesmo método de comunicação entre processos, recursos do Kernel, etc), mas não está de acordo com o Especificação única do UNIX . Exemplos destes são variantes BSD, distribuições GNU / Linux e Minix. No final, está mais ligado a sua marca registrada e aos comportamentos do sistema.
UNIX era um sistema operacional originalmente desenvolvido pela AT & T nos anos 60. Era um sistema operacional de código fechado, então muitas pessoas clonaram sua funcionalidade para criar SOs semelhantes a UNIX como BSD e Linux . Outros Licenciados UNIX para criar seus sistemas operacionais, como AIX .
O UNIX tornou-se mais recentemente uma especificação para sistemas operacionais licenciados pelo Grupo Aberto . Eles precisam aprovar o sistema operacional antes que ele possa ser chamado de UNIX.