SGI compares Linux, Unix source code

An open letter to the Linux community published this week by Silicon Graphics indicates that SGI has conducted a comprehensive comparison of the Linux kernel and the Unix System V source code owned by The SCO Group.

According to the letter, authored by SGI Vice President of Software Rich Altmaier, SGI conducted an "exhaustive comparison" of the Linux kernel and the Unix System V source code, which turned up only "trivial" code segments that "may arguably be related" to SCO's software.

The letter also disputed SCO's claims that SGI inappropriately contributed its XFS (eXtensible File System) code to the Linux operating system.

For months SCO has claimed that an exhaustive examination of the Linux source code has revealed software that has been copied line-by-line from its Unix System V code base. The Linux community has denied these allegations, but until this week no one else had claimed to have undertaken a comprehensive comparison of the two operating systems.

SGI's letter was published just as SCO revealed that it had threatened to terminate SGI's Unix license, alleging that the Mountain View, California, computer maker inappropriately contributed source code to Linux. Earlier this year, SCO announced that it had terminated IBM's AIX license, citing similar allegations. The Lindon, Utah, company is now engaged in a $3 billion lawsuit with IBM over the matter.

SGI's code comparison was done during September using the Comparator software created by open source advocate Eric Raymond, as well as some other internally developed tools, according to SGI. It compared source code from the Unix System V release 4.1 software that SGI has licensed from SCO with a version of the Linux kernel released this June, SGI said.

"Our review was focused on the code we contributed to Linux; however, we did run the Comparator code on the Linux 2.4.21 kernel. The process involves using subjective judgment to review similarities identified by the tool," said Greg Estes, SGI's vice president of corporate marketing, in an e-mail response to questions.

The point of SGI's comparison was to search for any potential matches between Unix System V and any contributions that SGI made to the Linux kernel, not to vet the software for the entire community, Estes said in an interview. "We are not making any kind of representation at all about anybody else's contributed code," he said.

SGI first reviewed its open source contributions earlier this summer, and Altmaier's letter concedes that SGI discovered at that time that three "brief fragments" of SGI-contributed code matched the Unix System V code that SGI had licensed from SCO.

"All together, these three small code fragments comprised no more than 200 lines (of code)," wrote Altmaier. "It appears that most or all of the System V fragments we found had previously been placed in the public domain, meaning it is very doubtful that the SCO Group has any proprietary claim to these code fragments," he added.

The code in question was no longer in the core Linux kernel, following the Aug. 25 release of Linux 2.4.22, Altmaier wrote.

Then in September SGI carried out its more comprehensive comparison. "SGI continued our investigation to determine whether any other code in the Linux kernel was even conceivably implicated," Altmaier states in the letter.