Easiest way to get a small VM disk image?

[Rodney W. Grimes]

> Hello,
> 
> I want to build an OpenNebula[1]-compatible VM image of FreeBSD 11.1. One
> requirement for my use case is that the image should initially be small
> (not as in "take up little physical space", but as in "the size of the
> virtual disk as visible in the VM should be small". Specifically, I want
> the virtual disk size to be no more than 3GB (which should not be a
> problem, as the default installation of FreeBSD takes a lot less than 3G).
> 
> The VM images available in the official downloads have a virtual size of
> 20GB. Therefore I need to somehow build my own image (or shrink the
> existing ones). Here are the approaches I have thought about:
> 
> - Create and partition an empty disk image, rsync the contents of the
> official image into it. Problems: AFAIK requires a FreeBSD host to build
> (in order to be able to create a UFS filesystem); requires juggling around
> with loopback mounts and such. Probably still the most feasible option, but
> I am not sure, which is why I'm asking.
> - Create an empty image, boot it in a VM and install from an installation
> ISO. Problem: not sure how to automate; might not get 1:1 parity with the
> official VM image
> - Somehow shrink the existing image. Problem: How?
> - Find out how the official images are built and do that with a smaller
> size. This is where this list comes in :-)
> 
> Which (of these, or any other) is the easiest way to get a small image?
> 
> Thanks a lot!

Thought it still requires a FreeBSD host to do, somethink along the
lines of:
truncate -s 2G NEW_FreeBSD_vm_image
mdconfig -f OFFICIAL_FreeBSD_vm_image -u 100
mdconfig -f NEW_FreeBSD_vm_image -u 101
#You have to fdisk, bsdlabale and newfs /dev/md101 here to your needs
mkdir /tmp/output
mount /dev/md101s1 /tmp/output
cd /tmp/output
dump 0Bf 2000000 - /dev/md100s1 | restore rf - && rm restoresymtable

This was hand written here in vi, so probably has lots of sharp edges.

-- 
Rod Grimes                                                 rgrimes at freebsd.org