Thank Jonathan for all these clarifications.
I have just one concern
This is what is in /boot/efi/EFI/fedora/grub.cfg
menuentry 'Fedora 30 (Thirty) (on /dev/sdc3)' --class fedora --class gnu-linux
--class gnu --class os $menuentry_id_option
'osprober-gnulinux-simple-da1fb213-c138-4711-aba2-76a598506283' {
insmod part_msdos
insmod ext2
set root='hd2,msdos2'
if [ x$feature_platform_search_hint = xy ]; then
search --no-floppy --fs-uuid --set=root --hint-bios=hd2,msdos2
--hint-efi=hd2,msdos2 --hint-baremetal=ahci2,msdos2
9089ac44-babc-47c3-9fb5-a51a95931a7d
else
search --no-floppy --fs-uuid --set=root
9089ac44-babc-47c3-9fb5-a51a95931a7d
fi
linux /vmlinuz-5.0.16-100.fc28.x86_64
root=UUID=da1fb213-c138-4711-aba2-76a598506283 ro rd.md=0 rd.lvm=0 rd.dm=0
SYSFONT=True KEYTABLE=fr-latin9 rd.luks=0 LANG=en_US.UTF-8
initrd /initramfs-5.0.16-100.fc28.x86_64.img
}
Why there is still some tace of fc28 messed with fc30?
I could not remove kernel-core fc28 (the only kernel fc28 package)
===========================================================================
Patrick DUPRÉ | | email: pdu...@gmx.com
Laboratoire interdisciplinaire Carnot de Bourgogne
9 Avenue Alain Savary, BP 47870, 21078 DIJON Cedex FRANCE
Tel: +33 (0)380395988
===========================================================================
> Sent: Sunday, May 31, 2020 at 8:54 PM
> From: "Jonathan Billings" <billi...@negate.org>
> To: "Community support for Fedora users" <users@lists.fedoraproject.org>
> Subject: Re: boot/grub
>
> On May 31, 2020, at 04:41, Patrick Dupre <pdu...@gmx.com> wrote:
> > On a multi-boot PC, how grub is updated?
> > In the past /etc/grub2.cfg was updated.
>
> Specifically, with the legacy bootloader, it was /boot/grub2/grub.cfg that
> was updated, and the file in /etc was a symlink.
>
> > and now?
>
> If you use the legacy bootloader, it remains the same, but any modern x86_64
> hardware will use UEFI. So the grub.cfg is in /boot/efi/EFI/fedora/, along
> with the .efi executable for grub (and a signed shim EFI executable, for
> Secure Boot).
>
> > It seems that there are 2 tools: bootctl, and efibootmgr
>
> bootctl is part of systemd-boot, which is a different bootloader than GRUB2.
> By default on Fedora x86, GRUB2 is used.
>
> The ‘efibootmgr’ tool is used to interact with the computer’s UEFI firmware.
> The firmware is what launches on boot, and it is configured with efibootmgr
> with what EFI executable to launch. You need a fat32-formatted partition
> with the EFI label, which has an /EFI directory at its root. All
> UEFI-compatible firmwares can read those volumes and look for EFI executables
> within. So you can put a CentOS, Ubuntu, or Microsoft executable (or all of
> them!) and configure boot entries for each. There is a BootOrder EFI
> firmware variable that stores the order in which it chooses what to boot,
> depending on which is available. There’s the BootCurrent variable, as you
> mentioned, which shows what was last used to boot, and a BootNext which you
> can use to (temporarily) boot next boot.
>
> > What are the files managed by these tools?
> All EFI variables are stored in the EFI firmware. Linux makes them available
> as files in /sys/firmware/efi/. **DO NOT MESS WITH THESE FILES OR DELETE
> THEM**. You can brick your hardware if you do so. Just use the efibootmgr
> tool to change things.
>
> Once grub is launched, it reads the grub.cfg in the EFI directory. Modern
> Fedora doesn’t change the grub.cfg anymore, it reads data out of
> /boot/loader/entries/, where a grub.cfg fragment exists for each kernel.
>
> Remember when I mentioned that the EFI was a fat32 filesystem? Turns out
> that it’s a pretty unreliable filesystem and if the computer makes changes to
> it and is unceremoniously powered off, it will have a dirty bit set and the
> OS can’t even mount it when you start back up, causing boot errors and
> dropping you into the rescue shell. By putting a static grub.cfg into the EFI
> volume and all the changing entries into /boot/loader/entries, you’re only
> writing to a volume that is a journaled ext4 or XFS volume, which can be
> easily recovered. I believe that’s why there was the change.
>
> > Which tool is run after an update of the kernel?
>
> /bin/kernel-install is run with a bunch of parameters. It handles detection
> of what bootloader (grub legacy vs grub efi) and adding all the correct
> entries and may call tools such as grubby.
>
> There’s a bit more complexity to this but this is all I can remember off the
> top of my head and type on a mobile device. (It’s too nice outside here to
> get out of my hammock!)
>
> --
> Jonathan Billings <billi...@negate.org>
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