With Linux 4.0, you may never need to reboot your operating system again.
One reason to love Linux on your servers or in your data-center is that you so seldom needed to reboot it. True, critical patches require a reboot, but you could go months without rebooting. Now, with the latest changes to the Linux kernel you may be able to go years between reboots.
This is actually a feature that was available in Linux in 2009 thanks to a program called Ksplice. This program compares the original and patched kernels and then uses a customized kernel module to patch the new code into the running kernel. Each Ksplice-enabled kernel comes with a special set of flags for each function that will be patched. The Ksplice process then watches for a moment when the code for the function being patched isn’t in use, and ta-da, the patch is made and your server runs on.
Oracle acquired Ksplice in 2011, and kept it just for its own Oracle Linux, a Red Hat Enterprise Linux (RHEL) clone, and as a RHEL subscription service. That left all the other enterprise and server Linux back where they started.
Then KernelCare released a service that could provide bootless patches for most enterprise Linux distros. This program use proprietary software and is only available as a service with a monthly fee. That was a long way from satisfying many Linux system administrators.
So, Red Hat and SUSE both started working on their own purely open-source means of giving Linux the ability to keep running even while critical patches were being installed. Red Hat’s program was named kpatch, while SUSE’ is named kGraft.