Re: EFI boot partition overwritten

From: Warner Losh <>
Date: Fri, 16 Jul 2021 17:35:11 UTC
On Fri, Jul 16, 2021 at 6:14 AM Thomas Laus <> wrote:

> Group:
> This is an issue for more than just CURRENT.  The 'usr/src/UPDATING'
> file has the instructions for updating the ZFS bootblocks but not the
> EFI partition.  I recently upgraded a RELEASE-12.2 to RELEASE-13.0.  The
> freebsd-update procedure did not upgrade the ZFS bootblocks.  I forgot
> that this PC was UEFI only and overwrote the first partition with the
> gptzfsboot code.  That made my system un-bootable.  I found the recovery
> procedure on one of the FreeBSD forums and was able to reformat the EFI
> MSDOS partition, create the proper directory structure, and copy the
> loader.efi file to the correct location and filename using the Live
> Filesystem running on the installation CD.
> I searched the man pages and the UPDATING file for instructions but came
> up empty and had to resort to finding the answer on one of the forums.
> The filenames have changed since FreeBSD first supported EFI and some of
> the forum instructions are out of date.  My problem must be fairly
> common and the recovery procedure should be in a man page with a
> footnote or man reference somewhere on the install media.
> Since CURRENT receives more updates to the EFI boot loader than the
> release versions, there should be instructions in the CURRENT
> 'usr/src/UPDATING' file on how to update the EFI bootcode.

There should be. Yes. Last time I went hunting for a place to shoe-horn it
in, I got distracted by something else.

The instructions are relatively straight forward. I'm writing them here for
your benefit, and also in case someone wants to send me a diff/pull request
to include them. Or better yet, put this in the handbook and we can
a location from there.

WARNING: This is a quick run-through of how to do this if you need to.
The example commands given might not be exactly right for all installations
as differing numbers of partitions will change the '-i' parameters.

Frist, you need a partition that's of the right type. For GPT that type is
as shown in `gpart show <boot-device>` eg
# gpart show ada0
=>        40  2000409184  ada0  GPT  (954G)
          40        1600        - free -  (800K)
        1640  1992292792     2  freebsd-ufs  (950G)
  1992294432     7000000     3  freebsd-swap  (3.3G)
  1999294432     1114792     4  efi  (544M)

If you don't have one, you'll need to create one. In the above exmaple,
I had installed the system with a tiny partition for booting with legacy
BIOS, but then moved to booting with UEFI. I did this by turning off
swapping and doing the following:
# gpart resize -i 3 -s 7000000 ada0
I then created a new efi partition:
# gpart add -t efi ada0
and I let it autosize.

Next, I needed a FAT32 filesystem on that device. FAT16 usually will
work and often FAT12, but there are known examples of system integrators
that omit support for these last two (more the latter than the former since
it's viewed as a floppy only thing, and who uses floppies).  I just used
newfs_msdos and mounted it:
# newfs_msdos -F 32 /dev/ada0p4
# mount -t msdos /dev/ada0p4 /boot/efi

Next, you need to put a bootloader on the system. Unless you have
special needs, loader.efi is that loader.
# mkdir -p /boot/efi/efi/boot
# cp /boot/loader.efi /boot/efi/efi/boot/bootx64.efi

If you are using efibootmgr to set a location to boot from, generally people
create a freebsd directory (we've registered /efi/freebsd with the proper
to avoid conflicts):
# mkdir -p /boot/efi/efi/freebsd
# cp /boot/loader.efi /boot/efi/efi/freebsd
# efibootmgr -c -a -k /boot/kernel/kernel -l
/boot/efi/efi/freebsd/loader.efi -L "FreeBSD Boot"
though some vendors impose limits on how many boot envs you can create
and some do not allow any at all.