Linus Torvalds and Dirk Hohndel, vice president and chief of open source at VMware, discussed the role that GNU GPL played in the success of Linux during a keynote conversation this week at LinuxCon NA in Toronto. Here is an edited version of the conversation.

Hohndel, who has been involved with the kernel for a very long time, said that during the past 25 years there have been many challenges, and one of the biggest challenges was the possibility of fragmentation. "How do we keep one single kernel?" he asked.

"I used to be worried about fragmentation, and I used to think that it was inevitable at some point," said Torvalds. “Everyone was looking at the history of Linux and comparing it with UNIX. People would say that it’s going to fail because it's going to fragment. That's what happened before, so why even bother?"

What made the difference was the license. "FSF [Free Software Foundation] and I don't have a loving relationship, but I love GPL v2," said Torvalds. "I really think the license has been one of the defining factors in the success of Linux because it enforced that you have to give back, which meant that the fragmentation has never been something that has been viable from a technical standpoint."

That doesn't mean Linux is immune to fragmentation. Torvalds's greatest fear was that fragmentation would happen due to different markets. In the early days SGI was pushing Linux into 1,000 core machines, and Linux was not ready. SGI wanted to talk to Torvalds about how to manage that. "I said you should do your own big iron version of Linux and sell it as SGI Linux," he said. "They did to some degree, but they kept moving things back."

GNU GPLv2 allowed merging things back. "We ended up just improving to the point where our limits from the standard kernel went away and let the SGI people push their code to us, so that they had less headaches with all the changes they did," Torvalds said. "That experience just convinced me that, even if you have completely disparate machines and target markets, we really can have a single image from the source code standpoint."

GNU GPL vs. other licenses

GNU GPL is not the only open-source license out there. There are many more permissive licenses, like MIT and BSD, where you don't have to send back the modifications or improvements that you made to the software, unlike GNU GPL.

Torvalds said that most of the time projects started by companies show up under BSD or MIT licenses because it allows them to do anything with the project. "They see that as a big upstart," Torvalds said. "I think that if you actually want to create something bigger, and if you want to create a community around it, BSD license is not necessarily a great license."

While these licenses have worked very well for many companies, they do make it hard if you are looking for outside developers who don't feel protected by a big company. The company doesn't have to make any promises, because the BSD license allows both the company and the outside developer to do anything they want with the code. That doesn't provide a warm fuzzy feeling.

A developer would feel that the big company is going to take advantage of their work, said Torvalds. "The GPL ensures that nobody is ever going to take advantage of your code. It will remain free and nobody can take that away from you. I think that's a big deal for community management."

"Over the years, I've become convinced that the BSD license is great for code you don't care about," Torvalds said. He also pointed out that choosing a license for your project is a personal choice. "Some people love the BSD license. Some people love the proprietary licenses. I understand that. If you want to make a program and you want to feed your kids, it makes a lot of sense to have a proprietary license and sell binaries. I think it makes less sense today, but I really understand the argument. I don't want to judge. I'm just giving my view on licensing."

Growing together

As much as GPL helped Linux, in return, Linux also helped GPL. Karen Sandler, the executive director of the Software Freedom Conservancy said at LinuxCon that the success of Linux during the past 25 years has been proof of the concept of copyleft. "I would like to see that extended to more free and open source software projects," she said. "The full experiment of copyleft has never really been tried."