Install new kernel for frugal install

[thomasl]

(If there are errors or omissions, feel free to tell me or edit this post.)

To install and boot into a new kernel on a frugal system with root persistence (I think this should also work with home persistence?):
0. Remember that if you backup initrd.gz, vmlinuz, linuxfs and rootfs in your frugal boot directory nothing that you do in steps 1 to 10 can harm your current setup.
1. Boot and make sure that your rootfs has at least 750MB free space if you want to save state in step 5.
2. Install the new kernel via MXPI > Popular Applications > Kernels.
3. The freshly downloaded kernel will not yet be visible in live-kernel-updater. It seems the kernels to choose from within live updater do have to reside in linuxfs.
4. So to see and install the new kernel you have to remaster first with live-kernel-updater. Just follow the prompts to remaster. This produces a linuxfs.new file in your frugal boot directory but it does not yet change the kernel (ie the vmlinuz file) in frugal boot directory.
5. Run persist-save to save the downloaded kernel. This is not strictly necessary if the remastering and kernel update in steps 8/9 work but it keeps the current state in rootfs if that doesn't work.
6. Reboot into the newly remastered linuxfs.
7. After booting, the old kernel is still active but now you will see the new kernel in the live-kernel-updater screens.
8. Update "from" the old kernel within live-kernel-updater. You will see any new kernel choices only after you have chosen this option.
9. This will replace vmlinuz (ie the old kernel) and initrd.gz in the frugal boot directory with the new kernel and a new initrd.gz, saving the old files in *.kold.
10. Reboot and (hopefully) enjoy.

[dolphin_oracle]

this line isn't 100% accurate:

To install and boot into a new kernel on a frugal system with root persistence (I think this should also work with home persistence?) that is not booted via a Grub2 menu:

the process is the same weather you use grub or not. you just need to be running your frugal system. you boot loader doesn't matter. (in fact, our legacy live boot loader is syslinux)

[thomasl]

the process is the same weather you use grub or not. you just need to be running your frugal system. you boot loader doesn't matter. (in fact, our legacy live boot loader is syslinux)

I was under the impression (which may be way off) that if you boot with grub2 there's an Advanced menu that allows to boot into other kernels w/o having to go through step 8/9. But if I think about it probably this menu exists only for installed systems and not in frugal systems. In which case for a frugal install, however it's booted, this step is a must. If you can clarify this, I'll edit the offending line.

[dolphin_oracle]

the process is the same weather you use grub or not. you just need to be running your frugal system. you boot loader doesn't matter. (in fact, our legacy live boot loader is syslinux)

I was under the impression (which may be way off) that if you boot with grub2 there's an Advanced menu that allows to boot into other kernels w/o having to go through step 8/9. But if I think about it probably this menu exists only for installed systems and not in frugal systems. In which case for a frugal install, however it's booted, this step is a must. If you can clarify this, I'll edit the offending line.

as you suspect, the "advanced" menu is only for installed systems.

[thomasl]

OK, edited OP.