I want to really understand System V, the main origin of Unix (not Unix-like nor modified Unix to Linux). The main origin which is very confusing and not really with care its written somewhere.

Is it true FreeBSD is not Unix? But what is Unix or where is it then? Where can I find the origin source code to read it and see how the legend was born.


Follow up:



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    Last time I looked (which was admittedly back in 1992 or so) a source code license to AT&T System V would run you over $10,000. – Paul Tomblin Feb 13 '12 at 18:17
  • That was probably the educational license price which had a lot a restrictions. Full System V source code license was between $100,000 and $200,000 around that time, plus per user royalties. – jlliagre Feb 14 '12 at 22:25
  • The folks at MIT have an Xv6 system for teaching operating systems, which is essentially Unix v6 ported forward to modern C. Stumbled upon it the other day, is on my todo list... – vonbrand Jan 23 '13 at 3:51

"is UNIX" is a complicated thing - basically, FreeBSD can't say it's Unix because Unix is trademarked & they don't have the appropriate license. It also isn't derived from System V code, which is the direction the master Unix sources took.

Some old versions of Unix do now have source code available - notably Unix Version 7, one of the last PDP-11 versions. The Unix Tree has browsable source code for V7 and several other Unix distributions.

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    Beyond being a trademark, Unix is a standard. Should FreeBSD successfully pass the compliance test, which is a long and somewhat expensive process, it could claim it is Unix. – jlliagre Feb 14 '12 at 15:55

The only open source System V based Unix is OpenSolaris (and forks like Illumos / OpenIndiana).

It has strongly evolved since the early System V release but there still are pieces of code and algorithms identical or very similar to SVR4.0 and older.



AT&T Unix System V is not open source, so you can't get it.


It's nearly impossible to give a concise answer to what is Unix these days. In the early days BSD was a distribution of changes to Unix, extra features and ports to new platforms. Eventually, someone decided to distribute a complete package of BSD (derived from Unix) called 386BSD. Things happened and NetBSD and FreeBSD were born. Then the AT&T lawsuit stopped them from continuing. Most (but not all) original Unix code was removed and rewritten by the BSD folks at FreeBSD and NetBSD. Parts of FreeBSD are true Unix in a source sense.

SysV Unix diverged as well.. there are many modern Unix variants derived from it including Solaris, SCO Unixware (formerly Microsoft Xenix), etc. There's also divergences like MACH with Mac OS X being based on NeXTSTEP/OpenSTEP. The bsd family tree included in FreeBSD shows most of the divergences but does not include all of them.(MirBSD, MidnightBSD, ...)

SCO claims to own UNIX but courts ruled Novell has it. Novell sold the trademark to the Open Group and they sell a compatibility test suite and certification. Mac OS X, AIX and other things some people don't consider Unix are certified. At one point Linux was certified using the Open Group suite by IBM. Yet, Linux is considered a clone of Unix.

This becomes a religion question from here. Is it the source, the certification, the history... you decide.

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