[systemd-devel] howto switch from grub2-bios to systemd-boot

[Lennart Poettering]

On Mo, 22.06.20 16:01, Reindl Harald (h.reindl at thelounge.net) wrote:

> what is the best way to get a Fedora using legacy-boot to UEFI and at
> the same time switch from grub2 to systemd-boot?
>
> * how to get in installed from a live-iso to
>   the existing setup on disk
> * how to get the config files right at the first try
> * how does it work with kernel-updates
> * how to get GRUB_CMDLINE_LINUX over
> * is it possible to not kill grub2 for the time beeing
>   to boot back into BIOS-mode in case of emergency

we should probably write this down somewhere in clean form, but
basically what you have to do is this:

0. Remove grub, grubby and all that stuff
1. Mount your ESP to /boot, /efi or /boot/efi
2. If you have it mount your XBOOTLDR partition to /boot (consider
   changing your partition type uuid of your pre-existing /boot
   partition to the XBOOTLDR one, if you have it)
3. Run "bootctl install"
4. Manually invoke "kernel-install add" for all kernels that are
   currently installed.

The 4th step is only necessary because the grub RPM fucks up the
kernel-install script systemd ships and generates snippets that are
invalid. After removing grub you thus need to rerun "kernel-install"
to regenerate the correct snippets.

In an ideal world Fedora would just use boot loader spec compliant
snippets anyway, so that step 4 wouldn't be ncessary. And step 1+2 would
not be necessary either, if everything is was mounted and tagged
properly from the beginning.

Kernel command line you can configure in /etc/kernel/cmdline. That's
where kernel-install picks it up. When you change that file, rerun
kernel-install for the relevant kernels.

> can /boot holding the kernel itself still be a Linux RAID1 or classical
> ext4 partition or is it required that the kernel and initrd live on the
> EFI partition too?

No, that's not supported in sd-boot. A boot loader is a boot loader,
it should contain a fragile storage stack. It's kinda what sd-boot is
supposed to do better than grub.

Lennart

--
Lennart Poettering, Berlin