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Just like Ubuntu, Arch, Red Hat etc are just modifications to the original Linux Kernel... macOS (XNU), Solaris etc are some variants of the closed source code of AT&T's UNIX. But what is the purest UNIX kernel or distribution, per se?

Is the UNIX kernel code (the original one) completely lost? Or is it still being maintained by someone (AT&T)?

If there is an up-to-date nothing-except-the-kernel-source-code? How can I get my hands on it? (I obviously intend to pay) Is it available under personal/student license or do I need to buy a business license?

P.S. I have a limited knowledge about UNIX.

marked as duplicate by muru, taliezin, A.B, Christopher, Thomas Dickey Jun 12 at 22:37

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  • One of the BSD releases perhaps? – ivanivan Jun 12 at 12:33
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FreeBSD is likely the most directly-derived modern UNIX-based OS. In June of 2017, Diomidis Spinellis of the Athens University of Economics and Business published a research paper which documents the evolution of the Bell Labs UNIX codebase from its early beginnings through to the modern-day FreeBSD 12. Using a variety of sources and methods, he essentially reconstructed a Git repository timeline which traces current-day FreeBSD back to epochal origin of UNIX.

The project has achieved its major goal with the establishment of a continuous timeline from 1970 until today. The repository contains:

  • snapshots of PDP-7, V1, V2, V3, V4, V5, V6, and V7 Research Edition,
  • Unix/32V,
  • all available BSD releases,
  • the CSRG SCCS history,
  • two releases of 386BSD,
  • the 386BSD patchkit,
  • the FreeBSD 1.0 to 1.1.5 CVS history,
  • an import of the FreeBSD repository starting from its initial imports that led to FreeBSD 2.0, and
  • the current FreeBSD repository.

The files appear to be added in the repository in chronological order according to their modification time, and large parts of the source code have been attributed to their actual authors. Commands like git blame and git log produce the expected results.

In particular, Figure 5 of the paper documents the proportional provenances of the codebases comprising several Berkeley UNIX milestone releases.

I recommend his paper highly to anyone interested in the historical evolution of UNIX and BSD. The GitHub page for the project is also interesting reading.

  • That does not prove in any way that FreeBSD is more similar to the original Unix than eg. NetBSD or a SysV derived system like Solaris. Also, the fact that is basically tracks a single branch makes it pretty useless for finding the origin and evolution of features like named pipes or /proc filesystem – pizdelect Jun 12 at 21:56

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