Linus Torvalds, who was then a student at the University of Helsinki in Finland, developed Linux in 1991. He released it for free on the Internet. Due to the far reach of the Free Software Foundation (FSF) and the GNU Project, Linux popularity increased rapidly, with utilities developed and released for free online. A commercial version of Unix was released by RedHat in the early 1990’s (combining the OS with technical support and documentation) and the popularity of Linux continued to skyrocket.
A system is termed UNIX only if it complies fully with (and is certified by) the Single Unix Specification (SUS) standards. Similar systems that do not comply fully or are not certified, such as Linux, are termed “Unix-like” operating systems
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