Re: EFI boot partition overwritten

From: Michael Gmelin <>
Date: Fri, 16 Jul 2021 22:13:13 +0200
> On 16. Jul 2021, at 19:38, Warner Losh <> wrote:
> ´╗┐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 the forum instructions are out of date.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
> reference
> 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
> `efi`
> 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
> folks
> 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.

It would be cool to also update the loader.efi man page to be a bit more useful (this is what 'zpool upgrade' refers to/will refer to in the future).


> Warner
Received on Fri Jul 16 2021 - 20:13:13 UTC

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