An open letter to the Linux community published this week by Silicon Graphics indicates that the company has conducted a comprehensive comparison of the Linux kernel and the Unix System V source code owned by the SCO Group.
The letter said SGI has 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 licence, alleging that the computer company had inappropriately contributed source code to Linux.
Earlier this year, SCO announced that it had terminated IBM's AIX licence, citing similar allegations. SCO is now engaged in a $3bn lawsuit with IBM over the matter.
SGI carried out the code comparison last month using the Comparator software created by open-source advocate Eric Raymond, as well as some other internally developed tools. It compared source code from the Unix System V release 4.1 software - which SGI has licensed from SCO - with a version of the Linux kernel released in June.
"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.
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.
SGI first reviewed its open-source contributions earlier this summer, and vice president of software Rich Altmaier has conceded in the open letter that SGI discovered at that time that three "brief fragments" of SGI-contributed code matched the Unix System V code 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 25 August 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 wrote.
This comparison revealed a few examples of line-by-line copying, but did not determine whether the code was owned by SCO or in the public domain, according to the letter.
"SGI has discovered a few additional code segments ... that may arguably be related to the Unix code," Altmaier wrote. He added that these segments were "trivial in amount".
SGI declined to reveal any details on the additional code segments it found, but the fact that its analysis appears to reveal no extensive overlap between the code in Linux and System V is good news for Linux users, according to Gartner analyst George Weiss.
"I think it's very helpful," he said. But more information is needed to respond to SCO's copyright allegations fully, he added. "I don't know if the job is complete from this letter."
It would be more helpful if other SCO licensees, such as Hewlett-Packard IBM performed similar analyses and went public with their results, Weiss added.
Such a thorough vetting of the Linux code might answer questions about line-by-line copying, but it would not counter all of SCO's charges, Weiss said.
SCO claims that Linux also contains derivative works built on top of its System V Unix, such as the XFS code that SGI contributed to Linux, as well as "obfuscated" code that is almost identical to SCO's Unix. These claims would not be answered by the kind of analysis that SGI has done, he said.
Weiss praised the tack SGI has taken with its letter, saying that Altmaier's response has helped mitigate SCO's allegations. "I thought it was one of the best responses [to SCO] that I had seen. Instead of getting deeply offensive and heaping abuse on SCO, they took a more productive approach, attempting to see what the claims might be," he added.
The fact that SGI has replaced the three code fragments in question does not satisfy SCO, according to Blake Stowell, a SCO spokesman. "These releases have already taken place in Linux. You still have all these machines out there that haven't applied patches that are still benefiting from this Unix System V code."
Any line-by-line contribution of SCO's code to Linux was "not trivial", he added.
Robert McMillan writes for IDG News Service