Cannot boot after 2nd install

Hello, I have a fedora which was running fine fine on /dev/sdb (/boot/efi on /dev/sdb1) Then I install a new fedora 30 on /dev/sda6 (also with /boot/efi on /dev/sdb1) When I rebooted, the "old" machine did not show up (at grub), then I run grub2-mkconfig -o /boot/efi/EFI/fedora/grub.cfg Now "old" machine is recognized at grub, but I get an error at the boot time I cannot even run a command line (like system*) Actually, I get Failed to mount /boot/efi Should I run: grub2-install /dev/sda or grub2-install /dev/sdb Also, when booting (before grub), I have options /EFI/BOOT/BOOTx64.EFI (this on let be boot on the new install) /EFI/fedora/grub.cfg /EFI/fedora/shimx64.efi Which one should I use preferentially? Thank =========================================================================== Patrick DUPRÉ | | email: pdupre(a)gmx.com Laboratoire interdisciplinaire Carnot de Bourgogne 9 Avenue Alain Savary, BP 47870, 21078 DIJON Cedex FRANCE Tel: +33 (0)380395988 ===========================================================================