Ubuntu – Updating kernel versions when booting from rEFInd

See this bug: https://bugs.archlinux.org/task/16702#comment80122

And this blogpost: http://losinggeneration.homelinux.org/2009/10/16/why-arch-linuxs-kernel-upgrades-suck/

So far I haven't found a good solution, but I will update if I do.

One thing to keep in mind beyond grub, the kernel, and initrd is /usr/lib/modules/. When the linux package updates the old package deletes it's folders in /usr/lib/modules/ and the new kernel adds its new modules. If you want both kernels working, you're going to want both sets of modules. And /usr/src/ contains the kernel headers (needed to build new modules, such as the nvidia drivers), so you'll probably want to keep those, too.

The steps I guess would be something like:
1. Detect linux package is going to be upgraded.
2. Backup what it's going to delete on uninstall (/usr/src/$(uname -r), /usr/lib/modules/$(uname -r), /boot/{vmlinuz-linux,initramfs-linux.img,initramfs-linux-fallback.img})
3. Let pacman do its upgrade
4. Restore everything in 2 (probably giving a new name to the stuff in /boot
5. Edit grub or whatever.

Alternate steps (somewhat less good)
1. Let pacman update
2. Detect kernel was updated
3. from /var/cache/packman/pkg/linux-${previous_version}-pkg.tar.xz extract /usr/src/, /usr/lib/{modules,extramodules}, and /boot/vmlinuz (renaming the one in /boot, obviously)
4. run mkinitcpio with the -k option to build the old init
5. Edit grub or whatever

In this alternate method, you loose your 3rd party modules (virtual box, ATI/Nvidia, etc), but it might be something you could run from cron and automagically detect kernel updates have occured.

You're advised to read EFI bootloader principles -- this should help you understand that installing a bootloader into MBR or a partition's boot sector is not going to do anything when booting in EFI mode. You basically want to establish or reuse an existing ESP (EFI System Partition) on a GPT partitioned disk and to store all of your bootloaders in its subdirectories.