Who is responsible for the Linux kernel?

Question

As of today, there are many Linux distributions like Ubuntu, Fedora, Gentoo, Mint, Debian, etc. These distributions update at different cycles. Ubuntu seems to update its kernel weekly or monthly, while Debian is reluctant to update the kernel.

I am wondering whether these distributions maintain their own kernels. Or do they just get the original kernel code from Linus Torvalds, modify it a little bit as need, and then release their revised kernel with their package management system?

Do all the distributions use the same kernels from Linus Torvalds? If it is the case, why do different distributions update/release their kernels at the different cycles?

Answer 1

The distro kernels are all compiled from the official source, with distro specific patches applied. These patches are relatively minor compared to the scope of the kernel itself. As long as you know what you are doing, you can substitute a custom kernel into any of the mainstream distros, although this is discouraged since it may cause a mismatch with system header files; for that reason the distros usually release a kernel source package of their own so you can use that instead of the "vanilla" (official, unpatched) source if you want to compile it yourself.

why different distributions update/release their kernels at the different cycles

For the same reason they release all the other software at different cycles -- to ensure everything works properly with everything else. Different distros have different policies and goals in this regard. They may hurry to get a package out as soon as the upstream source is updated, they may maintain "testing" and "stable" streams, and they may use an independent schedule.

Answer 2

First of all, nobody "gets the kernel from Linus". Yes, Linus is still actively involved in the kernel's development and has final say in any disputes but he most certainly does not write it alone! The wikipedia page on the Linux kernel is quite good on the subject:

The kernel changes made in year 2007 have been submitted by no less than 1900 developers – but there may be a lot more because developers working in teams usually count as one. It is generally assumed that the community of Linux kernel developers is composed by 5000 or 6000 members. As of 2013, the 3.10 release of the Linux kernel had 15,803,499 lines of code; without a smart project management it would not be possible to keep such scale of development up and going.

Instead of a roadmap, there are technical guidelines. Instead of a central resource allocation, there are persons and companies who all have a stake in the further development of the Linux kernel, quite independently from one another:

People like Linus Torvalds and I don’t plan the kernel evolution. We don’t sit there and think up the roadmap for the next two years, then assign resources to the various new features. That’s because we don’t have any resources. The resources are all owned by the various corporations who use and contribute to Linux, as well as by the various independent contributors out there. It’s those people who own the resources who decide...

—Andrew Morton, 2005

Now, yes, most distributions maintain their own slightly different kernels. The stock kernel can be downloaded from http://kernel.org but each distribution will tweak it to suit their needs. Some change it more and others less, I'm sure some don't change it at all.

As for the update cycle that is simply a choice the distributions make, they can update as often or as rarely as they like. Distributions like Debian that aim for rock solid stability, update rarely while those that like to be on the cutting edge like Arch, update often.