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Date: Sun, 17 Nov 2013 21:49:50 +0000
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From: "Thomas Mueller" <mueller6724@bellsouth.net>
To: freebsd-questions@FreeBSD.org
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Subject: Re: how install two freebsd9.2 on one disk?
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> for some reason, i want to install two freebsd9.2 OS on one SSD. is it
> possible?? i have problem in partitioning my disk for two OS. you know
> there is just one ada0 which can be partitioned.
> if i define more partitions on ada0, can i use some of them for the first
> OS and the others for second one? if yes, how can i manage booting?
> how and where should i install boot manager in order to manage them in
> booting time??
         
> any comments or hints are appreciated
> SAM

If you use GPT, you will need a FreeBSD boot partition unless you have some other method of booting from a USB stick.

Are the two FreeBSD installations for the same architecture or two different, like maybe amd64 and i386?

Grub2 can't boot FreeBSD 9.1 and 9.2 as it does with FreeBSD 10.0-STABLE and 11.0-HEAD.

set root=(hd0,gpt2)  # or wherever it is
insmod ufs2
kfreebsd /boot/loader
boot

But if you can boot one, you may be able to boot the other.

If architecture and kernel are the same, escape to loader prompt and 
boot -a
This will ask for root partition, such as
ufs:/dev/ada0p2 (or wherever it is)

If the kernel is different, copy from second installation to a different subdirectory on the first, and/or give the kernel a different name.

Then, at the loader prompt, 
unload
boot /path-to-second-kernel -a
and specify the root partition at the mountroot> prompt.

I have done this, but have not tried this on crossover between amd64 and i386.

Tom