Even many Linux users aren’t aware that there are many different kinds of Linux kernels. Sure, there’s the eternal release candidate kernels, which Linus Torvalds is perpetually working on, but then there are the ones we use every day on our desktops, servers, and clouds. Of these, the most important one for hardware designers and programmers are the long-term support (LTS) kernels. So, when their chief maintainer, Linux kernel developer and leader Greg Kroah-Hartman, says, “#Linux 5.10 will be the next Longterm (aka LTS) #kernel (and thus supported for at least two years, but, in the end, it often is six).” It’s a big deal.
There’s nothing that special about the forthcoming Linux 5.10 kernel. True, an ancient memory feature, which dates back to when 286 processors hummed inside out computers, have been taken out. But, so far, there are no important new features, such as Linux 5.6’s WireGuard, included. We can expect 5.10 to see the light of day in December 2020.
No, 5.10’s real importance comes from the simple fact that it is an LTS version.
An LTS includes back-ported bug fixes for older kernel trees. Not all bug fixes are imported. But all the important ones are backported to such kernels. They, especially for older trees, don’t usually see very frequent releases. LTS’s point is to make it easier for developers, especially of devices, to use Linux without worrying about security problems discovered long after a kernel’s been released. That’s vital for Linux-based device engineers because they can take years to build a single gadget.
Current, as of October 2020, Linux LTS Kernels
What makes this release even more interesting is that the Android open-source project (AOSP) is getting ever closer to being able to boot and use the mainline Linux kernel. With Linux 5.10, Android may finally be a pure Linux distribution, rather than a very close cousin.
Altogether there are five different types of Linux kernel releases: Prepatch or release candidates (RC), Mainline, Stable, LTS, and the various Linux distribution kernels.
RC must be compiled from source and contains bug fixes and new features. These are maintained and released by Linus Torvalds.
Torvalds also maintains the Mainline tree, which is where all new features are introduced. New mainline kernels, such as 5.10, are released every few months.
When the mainline kernel is released for general use, it is considered “stable.” Bug fixes for a stable kernel are back-ported from the mainline tree and applied by a designated stable kernel maintainer. Typically, there are only a few bug-fix kernel releases until the next mainline kernel becomes available.
Each Linux distribution maintains its own take on the kernel. So, for example, Red Hat Enterprise Linux (RHEL) kernel isn’t quite the same as SUSE Linux Enterprise Server (SLES) and so on.
The LTS are unique because they’re the only ones in which serious security patches are always backported. Each is guaranteed to be supported for at least two years, but it’s common for them to be supported for six years.
