Sun is no more, having been gobbled up by Oracle in 2009, and Allison claims its demise was driven by its inability to adjust to the growing power of open source software.

In a blog post earlier this month, Allison wrote: "Sun hated Linux. They complained that it was destroying the value of UNIX. Why buy an official UNIX when you could get the same thing for free via Linux distributions. Who would maintain this 'free' product? If everyone was working on a 'free' product, who would pay developers to maintain it?"

His post was prompted by Red Hat's decision on 21 June to announce that from that day onwards, only those who bought RHEL licences from the company would have access to the distribution's source code.

As background, a project named CentOS was distributing RHEL without Red Hat's trademarks — the only proprietary bits — until Red Hat bought the project and took it in-house in 2014. In December 2020, Red Hat shut down the CentOS project and created a development stream called CentOS Stream.

Red Hat's move has led SUSE to announce it would put more than US$10 million (A$14.8 million) to develop a fork of RHEL. Oracle has taunted Red Hat about the move, while AlmaLinux, set up after the December 2020 announcement, has said from now on it would only seek ABI compatibility with RHEL due to the difficulty in obtaining source code.

Questions have also been raised as to whether Red Hat's actions have violated the terms of the GNU General Public Licence, the licence under which Linux is released.

Allison, who has always been an ardent supporter of free software — the term for all open source until the term itself was invented sometime in 1998 — wrote that Sun claimed their UNIX — known as Solaris — was superior. "They claimed their UNIX had fewer bugs. They claimed their UNIX was better supported. They claimed their UNIX had better performance. In the beginning, all of these things were true, of course."

But all these attributes did not matter in the long run. "It didn’t matter. Linux ended up crushing Solaris and 'official' UNIX. The reason was that free and open source Linux distributions provided one great value to customers that 'official' UNIXes could not," he explained.

"That was freedom for the users. Linux was free to use. Linux was free to deploy. Linux was open to all users to modify and develop. Eventually, Sun realised this value and released Solaris under an open source licence (although deliberately incompatible with Linux so no code could be shared).

"It was too late. A once-great company, Sun was picked up by Oracle. Not even for its operating system business, but mostly for the Java language. Solaris is now a footnote in history, along with all the other proprietary UNIXes—except for IBM’s AIX. IBM knows a thing or two about maintaining legacy operating systems. That might stand them in good stead in the future; who knows?"

IBM is now the owner of Red Hat, having picked up the company for US$34 billion (A$50.5 billion) in 2019.

Allison, who now works for CIQ, a company that supports Rocky Linux, a clone of RHEL, said distributions that were compatible with RHEL made up the enterprise Linux system. "Users who deploy enterprise Linux can migrate between versions at will, keeping their costs low and choosing the support models that work best for them," he said.

"Cygnus Solutions, which created the original free software business model for support, understood this. I worked there, too, before Red Hat acquired them. As the software is under an open source licence, the value is in the maintenance and long-term support for code that can be shipped and worked on by anyone with the skills to do so.

"Sometimes that’s the users themselves, in which case they don’t need a support contact, only the freely available open source itself."

He said Red Hat's recent move to restrict access to the source code showed it was trying to eliminate any clones of RHEL, and make it only available from Red Hat.

"My advice to Red Hat management is to be careful what you wish for," Allison warned, adding that Mike McGrath, Red Hat’s vice-president of Core Platforms, had claimed this would allow Red Hat to use that extra money to create new and innovative open source software and employ many more open source developers.

"Maybe. But having been in the industry for a long time, my suspicions are that IBM shareholders might have other uses for that money," Allison said. "More likely, in my opinion, is that users, who value freedom and control over their own computing destiny more than anything else, will swiftly migrate off the RHEL platform.

"Where will they go? That’s where my crystal ball isn’t so good. Maybe some will go to Debian and derivatives. Some will go to SUSE enterprise Linux. The short-sighted ones will migrate workloads back to the welcoming arms of Microsoft Windows, or, being more charitable about Microsoft (who really are quite an open source company these days), an enterprise Linux distribution running on top of Microsoft Azure.

"I also don’t imagine that Oracle Enterprise Linux, which right now is another 'rebuilder' of RHEL, will go quietly into that good night. Not really their style."

Allison said he hoped Red Hat would have a rethink about trying to squeeze out the "rebuilders” of RHEL, and not just because he worked for one (CIQ).

"I understand that Red Hat feels that rebuilding the exact source code they feel they have worked so hard to create and test feels to them like freeloading and cheating. They claim to have the metrics that show that an enlarged enterprise Linux ecosystem provides little benefit to them financially, as users are just wanting free 'stuff'. Competition is hard, especially with your own product," he added.

"Even if this is true, restricting access to source code goes against everything all the engineers I know in the open source community believe in. Ultimately, it just doesn’t work.

"Customers want flexibility and control in how they consume and deploy enterprise Linux systems. If they can’t get it from Red Hat or any of the rebuilders, they will go somewhere else. Maybe not immediately, but eventually RHEL will fade as the gold standard.

"The question is does Red Hat want to continue to be the leader in enterprise Linux, or do they want to be king of a walled garden? Enterprise Linux is bigger than any one company. Users deserve better choices than being asked to forgo the freedoms guaranteed to them by open source."