Booting from USB on RPI3

[Mark Millard]

On 2020-Apr-23, at 13:32, Jonathan Chen <jonc at chen.org.nz> wrote:

> On Fri, 24 Apr 2020 at 08:22, Mark Millard <marklmi at yahoo.com> wrote:
> [...]
>> The RPi3 will not start to boot from a gpt partitioned
>> media. So picking gpt labeling as the example is somewhat
>> misleading for single-media booting. glabel based
>> labeling would be more realistic for the context.

Note the "single-media booting" reference above.

> The OP is attempting to boot off an external USB drive via loader.env.
> So it's the external drive's partitioning system that is of interest.
> FYI, my RPI3 boots off a GPT partition fine:
> 
> 1.topaz:~,8:30am# uname -a
> FreeBSD topaz.inside.chen.org.nz 12.1-STABLE FreeBSD 12.1-STABLE #0
> r358927: Sun Mar 15 22:24:30 NZDT 2020
> jonc at onyx.inside.chen.org.nz:/xbuilds/rpi3/obj/usr/src/arm64.aarch64/sys/GENERIC
> arm64
> 1.topaz:~,8:30am# gpart show -l da0
> =>       40  976773088  da0  GPT  (466G)
>         40       8152       - free -  (4.0M)
>       8192  964689920    1  topaz-root  (460G)
>  964698112   12075016    2  topaz-swap  (5.8G)
> 
> 1.topaz:~,8:30am# cat /etc/fstab
> # Device                Mountpoint      FStype  Options         Dump    Pass#
> /dev/gpt/topaz-root     /               ufs     rw              1       1
> /dev/gpt/topaz-swap     none            swap    sw              0       0
> 

That does not appear to have the msdosfs/EFI material
on the USB drive. So I'd guess that you are using
the microsd card for that: 2 media overall, not
single-media.

I also use a form of two-media instead of single-media
and use gpt on the USB media:

# gpart show
=>       63  249737153  mmcsd0  MBR  (119G)
         63      16380          - free -  (8.0M)
      16443     131040       1  fat32lba  [active]  (64M)
     147483        997          - free -  (499K)
     148480  241172480       2  freebsd  (115G)
  241320960    8416256          - free -  (4.0G)

=>        0  241172480  mmcsd0s2  BSD  (115G)
          0  230686720         1  freebsd-ufs  (110G)
  230686720   10485760            - free -  (5.0G)

=>       40  468862048  da0  GPT  (224G)
         40       2008       - free -  (1.0M)
       2048  413138944    1  freebsd-ufs  (197G)
  413140992    6291456    2  freebsd-swap  (3.0G)
  419432448    6291456    4  freebsd-swap  (3.0G)
  425723904   43138184       - free -  (21G)

# df -m
Filesystem               1M-blocks  Used  Avail Capacity  Mounted on
/dev/gpt/PINE642Groot       195378 34775 144973    19%    /
devfs                            0     0      0   100%    /dev
/dev/label/PINE64P2Groot    109101   219 100153     0%    /microsd_ufs
/dev/label/PINE642GAboot        63    43     20    69%    /boot/efi

I choose to have a copy of /boot on /microsd_ufs
and to use vfs.root.mountfrom="ufs:/dev/gpt/PINE642Groot"
in the loader.conf file in my context.

But such is not what Bob P. is trying to do from what
I can tell. He looks to be trying to avoid microsd
card media use if he can. He needs MBR on the USB
media for that (or some hybrid MBR that proves
compatibile).

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)