Solved. Re: Dualboot and ZFS

Warren Block wblock at
Thu Mar 22 13:28:23 UTC 2018

On Thu, 22 Mar 2018, Victor Sudakov wrote:

> Warren Block wrote:
>> On Mon, 19 Mar 2018, Victor Sudakov wrote:
>>> sysctl kern.geom.debugflags=0x10
>> Please reconsider doing this without it being required.  It means "allow
>> destroying mounted partitions" and is usually not necessary.
> It is recommended, or even required ("must") by the zfsboot(8) man page:

The vagueness here is from the "If the drive is currently in use".  It 
could easily be replaced with "If the user wants to destroy data from a 
drive that is currently being used".  I would argue that we should 
remove or rewrite that, as it is misleading.  Overwriting a drive that 
is "in use" is generally exactly the opposite of what people want.

>     zfsboot is typically installed using dd(1).  To install zfsboot on the
>     ada0 drive:
>           dd if=/boot/zfsboot of=/dev/ada0 count=1
>           dd if=/boot/zfsboot of=/dev/ada0 iseek=1 oseek=1024
>     If the drive is currently in use, the GEOM safety will prevent writes and
>     must be disabled before running the above commands:
>           sysctl kern.geom.debugflags=0x10
>     zfsboot can also be installed in an MBR slice:
>           gpart create -s mbr ada0
>           gpart add -t freebsd ada0
>           gpart create -s BSD ada0s1
>           gpart bootcode -b /boot/boot0 ada0
>           gpart set -a active -i 1 ada0
>           dd if=/boot/zfsboot of=/dev/ada0s1 count=1
>           dd if=/boot/zfsboot of=/dev/ada0s1 iseek=1 oseek=1024

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