On Fri, 27 Dec 2013, Mathieu Arnold wrote:

+--On 27 d├ęcembre 2013 10:28:07 -0500 Thomas Hoffmann <trh...@gmail.com>
| All the examples I've seen for updating bootcode assume GPT. If one has
| MBR (as I do) and assuming the following basic scheme:
| gpart show ada0
| =>       63  976773105  ada0  MBR  (466G)
|          63  976773105     1  freebsd  [active]  (466G)
| gpart show ada0s1
| =>        0  976773105  ada0s1  BSD  (466G)
|           0  943218736       1  freebsd-zfs  (450G)
|   943218736   33554369       2  freebsd-swap  (16G)
| would the equivalent bootcode statement be:
| gpart bootcode -b /boot/pmbr -p /boot/zfsboot ada0s1

No, the PMBR is for GPT partitioning only.

| where the boot code is /boot/zfsboot (rather than /boot/gptzfsboot) and
| ada0s1 is the slice on which FreeBSD is installed?

Hum, no, if you're using MBR and not GPT, you can't use gpart,

Why not? gpart is not GPT-specific. It handles MBR and BSDlabel bootcode correctly.

you have to
do something aweful like this :
# dd if=/boot/zfsboot of=/dev/ada0 count=1

That will overwrite the MBR partition table.

# sysctl kern.geom.debugflags=0x10
# dd if=/boot/zfsboot of=/dev/ada0 skip=1 seek=1024

That seems dangerous. I have not tried with zfsboot, but this should be close:

  # gpart bootcode -b /boot/zfsboot ada0
  # gpart bootcode -b /boot/zfsboot ada0s1

Untested! The first one may need to use /boot/mbr. A better way to do this, provided the system does not have a broken BIOS, would be to backup, repartition with GPT, and restore, avoiding the complication of multiple partitioning schemes.
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