At the most basic level, an operating system has to have:
Of course an operating system may have many other things that make it much more useful: a graphical user interface, drivers for different hardware, programs like office tools, graphics tools, etc. Not all operating systems need these other things — it depends on the focus of the particular OS.
In the linux OS:
So it is more precise to call most flavors of linux "GNU/Linux".
This is the primary site for the Linux kernel source, but it has much more than just Linux kernels.(Scroll down the page to see links to all the good info.)
The GNU Project was launched in 1984 to develop a complete Unix-like operating system which is free software: the GNU system. Variants of the GNU operating system, which use the kernel called Linux, are now widely used; (GNU is a recursive acronym for 'GNU's Not Unix'; it is pronounced
guh-noo, approximately like
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