Unix-like

Although there are general philosophies for Unix design, there is no technical standard defining the term, and opinions can differ about the degree to which a particular operating system or application is Unix-like.

Many popular applications, such as the Apache web server and the Bash shell, are also designed to be used on Unix-like systems.

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.

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 sublicensing of UNIX in 1979, a variety of proprietary systems were developed based on it, including AIX, HP-UX, IRIX, SunOS, Tru64, Ultrix, and Xenix.

Growing incompatibility among these systems led to the creation of interoperability standards, including POSIX and the Single UNIX Specification.

[18] Around 2001 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 POSIX-compliant, with Josey having prepared a list of differences between the POSIX standard and the Linux Standard Base specification,[19] but in August 2005, this project was shut down because of missing interest at the LSB work group.