[quote]there is no support for kernel maintenance through package management[/quote] may be true for the Ubuntu MATE distribution, but Arch and the recent Raspbian releases do kernel updates as part of “upgrade”. Former Raspbian releases required a “dist-upgrade”.
The current Raspbian cache contains:-
raspberrypi-bootloader_1.20161215-1_armhf.deb
raspberrypi-kernel_1.20161215-1_armhf.deb
[quote]there is no readily available knowledge base to consult as to what exactly constitutes a Pi kernel release in order to direct manual maintenenance[/quote] is unfortunately true. While https://github.com/raspberrypi/firmware contains kernels the process by which the Foundation decides a stable release is a mystery. Generally the kernel in the Foundation releases is quite stable.
[quote]there appears to be no ability to choose at boot time which kernel version to run[/quote] is true, although it is possible to swap kernels using the “kernel=” parameter in config.txt.
[quote]All of this contributes to making Pi kernel updating needlessly problematic. Simply moving forward by using only rpi-update to install the “latest and greatest” kernel is not a realistic option because recovery from a kernel update that fails to work properly is very difficult to do on a Pi. You can’t boot around a failing kernel, and no one seems to know how to restore the previous version. At a minimum it appears that one has to remove the SD card from the Pi, mount it on another Linux system, and do something, whatever that might be. There is also the matter of ever-accumulating detritus from defunct kernels.
The Pi updates produce a directory structure /boot.bak. Is rollback as “simple” as replacing the contents of /boot with what is stored in /boot.bak (which could require the use of another Linux system, if the latest Pi kernel does not run properly)? I can’t find any documentation that says so.[/quote]
The above seems to be an artefact of rpi-update, which is not intended for ordinary users, although for Ubuntu MATE this seems to be the only option.
Indeed the Foundation engineers warn about this “In normal circumstances there is NEVER a need to run rpi-update as it always gets you to the leading edge firmware and kernel and because that may be a testing version it could leave your RPi unbootable”. https://www.raspberrypi.org/forums/viewtopic.php?p=916911#p916911
Arch and the recent Raspbian releases do not leave “ever-accumulating detritus” (although the Former Raspbian releases did leave older modules).
I don’t know where this came from, I do not see it in my /boot/config.txt. kernel.img is the ARM6 kernel, so by definition unused by Ubuntu. Mind you , there seems to be no reason to remove it.