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

[Lennart Poettering]

On Fr, 04.09.20 21:41, Dave Howorth (systemd at howorth.org.uk) wrote:

> On Fri, 4 Sep 2020 17:44:23 +0200
> Lennart Poettering <lennart at poettering.net> wrote:
> > On Fr, 04.09.20 17:10, Reindl Harald (h.reindl at thelounge.net) wrote:
> >
> > > > 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.
> > >
> > > well, a boot loader should just *load* and not write anything so
> > > RAID1 is technically no problem and it shouldn't matter which of
> > > the 1, 2, 3 or 4 disks is there unless one survived.
> >
> > Robust boot loaders typically want to write boot counters to disk, so
> > that they can automatically revert back to older versions of the
> > OS/kernel if it doesn't boot. Thus some form of write access is
> > necessary if you care about robustness.
>
> But surely a boot loader of all things should never try to write to the
> place it is loading from? Booting should be idempotent (as long as it
> works, for sure). The only sane policy would seem to be that the loader
> had another path to a separate writable area?

UEFI provides file system access. Both read and write. Typically for
VFAT. Yeah, a boot loader should not modify the files it is itself
loaded from and also keep writes generally at a minimum, but counting
boots is generally the absolute minimum necessary, and can be
implemented by single sector updates in file systems such as VFAT. So
that's what sd-boot for example does.

Lennart

--
Lennart Poettering, Berlin