I may reboot my Linux systems once every six months. That's great for my personal use and a small business. For an enterprise, that's not good enough. Even twice-a-year reboots is twice a year too often for them. That's why Ksplice, which enables running systems to update even critical files without rebooting was so popular when it came out in 2009. Now, Oracle has bought Ksplice, and it appears it will be keeping it services available only for Oracle Linux.
Ksplice, according to its developers, "enables running systems to stay secure without the disruption of re-booting. Specifically, Ksplice creates re-bootless updates that are based on traditional source code patches. "These updates are as effective as traditional updates, but they can be applied seamlessly, with no downtime."
Ksplice does this by monitoring a computer's activity. When it determines that none of the CPUs or cores are doing any work, it takes over the system applies the patch, and then changes all function references both on the drives and in memory. Thus, when a program next calls for any patched functions it immediately finds and uses the updated ones.
While Ksplice itself is open-source software, and the service for individual users, under the old ownership was free, you'll need to pay a service fee if you're a business using Ksplice to keep your servers up-to-date. More to the point, and the annoyance of other Linux distributors, Oracle now states that "It will be the only enterprise Linux provider that can offer zero downtime updates, and expects to make the Ksplice technology a standard feature of Oracle Linux Premier Support."
That wouldn't be that easy to do though. While "Some Ksplice software … is available in source code form under the terms of the GNU General Public License and other open source licenses," not all of it is. In any case, it's not so much the program that would need to be forked. That would be relatively easy. But, forking the service would not be trivial. The Ksplice service provider must edit each patch for semantic changes to kernel data structures before applying the patches to a running Linux instance. This service could be duplicated, of course, but it's a job for a company, not just a few open-source developers.
I suspect one of the other major Linux distributors, Red Hat, SUSE, or Canonical, will do it. In the meantime, Oracle finally has a strong selling point in favor of its Linux for enterprise customers over its competitors.