Less than a week after Sun COO Jonathan Schwartz pledged to open source its Solaris operating system, the SCO Group has popped up to say that licence restrictions prevent Sun from contributing its work to the GPL. Solaris is based on Unix System V, the source code which has since been acquired by SCO.

SCO's marketing manager Marc Modersitzki said that although the company can't discuss specific details of its licence agreements, it is confident that Sun will be very rigorous in complying with its Unix System V licence, as the company defines its plans for open-sourcing any part of Solaris.

"While the details of Sun's plan to open-source Solaris are not clear at this time, Sun has broader rights than any other Unix licensee," Modersitzki said. "However, they still have licence restrictions that would prevent them from contributing our licensed works wholesale to the GPL."

Modersitzki said by spending more than $100 million in Unix licence fees, Sun has the broadest rights of any of SCO's Unix licensees and has been a licensee in good standing for many years. Although Sun has not publicly stated under which licence it intends to release an open source Solaris, Schwartz said: "Make no mistake, we will open-source Solaris." In an interview last month, Schwartz said "maybe we'll GPL it" and "We're still looking at that".

AUUG president and FreeBSD developer Greg Lehey said he can think of no evidence that would invalidate SCO's statement. "Unless Sun has an exclusive licence for the Unix code, which it obviously doesn't, it would find it difficult to change that licence," Lehey said. "I suppose the interesting question is if Sun releases those parts of Solaris which it has developed in-house, what does that do to the code it has licensed?"

Lehey said the GPL has the so-called "viral" effect, and that would theoretically cause the remainder to fall under the GPL as well, "but that's so preposterous that I can't think of any way it could happen".

"If there's any difference of opinion here, it would be more likely to be related to whether SCO agrees that Sun has written the code in question," he said. "We've already seen that SCO is very hazy about the origins of the individual components of its code base - witness its display of the Berkeley Packet Filter as 'its own work'."