Peter H. Salus & Eric Levenez Correct SCO's UNIX Chart

by Pamela Jones

June 20 2004

Talks_to_birds wrote to me, telling me about a project he's been working on, comparing the Eric Levenez chart [ ] with SCO's version [ ] and then each against UNIX historian Peter H. Salus' book, "A Quarter Century of UNIX."[1] He believed he'd found an error on SCO's chart.

That did not surprise me, because of my work on the Grokline [ ] project. I knew there were errors. But what he told me next, made me sit straight up. The error he spotted has to do with Minix, the very operating system the Alexis de Tocqueville Institution made such a fuss over (cf. here [ ] and here [ ]). SCO's UNIX chart seems to show a connection between Xenix/Sinix and Minix and Linux.

I immediately sent his email to Peter Salus and asked for his comment. He confirmed that talks_to-birds was right -- SCO's chart is not accurate in indicating such a connection.

Meanwhile, talks-to-birds wrote to Eric Levenez to ask him for his comment. Levenez also confirms that whatever SCO's chart may be trying to indicate, there is no connection at all between Sinix and Minix, and that the line from UNIX V7 to Minix on Levenez' chart is not because there is any V7 code in Minix, but merely because Minix was designed to be compatible with V7. There is a note beneath his chart, which reads: "Note 1 : an arrow indicates an inheritance like a compatibility, it is not only a matter of source code."

I now suspect AdTI's false accusation that Linus probably stole Minix code (which has been thoroughly repudiated and disproven) was no accident. Either they were fishing for information SCO could use at trial or they were misled by the chart into imagining such a connection and tried to "prove" it. Because others might be misled as well, here is the correction from Peter H. Salus and then Eric Levenez.


SCOG Goes Off the Graph
~ by Peter H. Salus

The Levenez UNIX timeline [ ] is a well-known resource about the evolution of UNIX operating system variants. Talks_to_Birds has pointed out what he calls "an interesting error" in a version of Levenez' timeline created by SCO:

TSCOG's error is found in one page of their version of the timeline, covering the period 1984-1986, at:

TSCOG has created a trail representing its "Linux" to "SCO Linux Pedigree" (green dots to a green solid line) that originates where "XENIX OS" forks downward off from UNIX Time Sharing System V7, and continues forward along the UNIX TSS lineage to a second downward fork at the origin of Siemen's Sinix, joined there by an upward fork from XENIX 3.0.

Continuing along, the green-dot-Linux pedigree folllows Sinix until it bends downward and joins a fork which descends to Minix.

And here is where the error lies: if one is to look at TSCOG's own graphics and compare it with Levenez' [ ], one can clearly see that the thin black line descending to Minix does *not* originate from the XENIX lineage at all, but rather starts one line upward, from the UNIX Time Sharing System continuation.

TSCOG apparently mistakes, or deliberately misinterprets, the fact that the crossing of two lines on Levenez' timeline does not represent a connection, but merely a graphic necessity.

It's as though TSCOG is attempting to use XENIX' relationship to Sinix to then incorrectly "climb on board" the connection from the UNIX TSS to Minix, and by doing so fabricating a relationship between XENIX and Minix/Linux that simply does not exist.

And, interestingly, TSCOG makes a very similar "mistake" on a Power Point slide for their SCOsource presentation [ ], on page 4, titled "The SCO Group Pedigree of Intellectual Property". Here the lines that TSCOG has drawn are so wide as to hide much of the detail, but if one compares this slide with Levenez' work, it's easy to see that again TSCOG is just "climbing on" to a fork that is not connected to the XENIX lineage but merely crossing it, albeit here without even bothering to include the Sinix relationship.

Of course, one can't be sure of TSCOG's actual intentions, but the graphic record that TSCOG has publicly available in two separate instances is clearly in error, however the error may have happened.

Talks_to_Birds is right. However, I don't think this is an innocent error at all: any more than I think that our friends at AdTI are innocent in their statements about the origins of UNIX, Minix or Linux.

By placing XENIX into the path leading to Minix, SCOG is fabricating an historical link. This fabrication then ties Linux (which is not a descendant of Minix) to XENIX and enables SCOG and AdTI to falsely manufacture a lineage.

Thanks, Talks_to_Birds. Our eyes are, indeed, everywhere.

Peter H. Salus

Email from Eric Levenez to talks_to_birds:

>SCO attempts to show a connection between the lineage of XENIX/Sinix
>and Minix by "climbing on board" a diagonal fork that is actually
>descending from the UNIX TSS lineage down to Minix, and does not
>originate with the Sinix lineage at all.

>In SCO's graphics this is depicted as a train of green dots that fork
>downward from the Sinix lineage along the line that is really
>descending from UNIX TSS.

I don't understand what SCO wants to say and how to interpret their
green line. For me there is no link at all between Sinix and Minix.

>I do not believe that this would correct: I am interpreting your
>graphic style, again, to *not* represent a connection at every
>crossing point.

>Am I correct in this interpretation?

Yes, of course. Only the end of a line, the triangle, is important.

For Minix, I have an arrow from V7 not because there is source code of
V7 in Minix, but because Tanenbaum writes in his book "Operating
Systems, Design and implementation" : "MINIX has been designed for
compatibility with Version 7 (V7) UNIX."


1. Dr. Salus, in addition to being the author of "A Quarter Century of UNIX", is also the author of several other books [ ], including "HPL: Little Languages and Tools", "Big Book of Ipv6 Addressing Rfcs", "Handbook of Programming Languages (HPL): Imperative Programming Languages", "Casting the Net: From ARPANET to INTERNET and Beyond", and "The Handbook of Programming Languages (HPL): Functional, Concurrent and Logic Programming Languages". There is an interview with him, audio and video, "codebytes: A History of UNIX and UNIX Licences" [ ] which was done in 2001 at a USENIX conference. Dr. Salus has served as Executive Director of the USENIX Association. He is also technical and historical adviser to the Grokline [ ] project, which is tracing ownership of UNIX with the goal of preparing an update to the Eric Levenez chart, one which will accurately reflect the ownership history of UNIX.

11:30 AM EDT

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