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README for vmdebootstrap
========================
`debootstrap` installs a basic Debian system into a directory, for use with
`chroot`(8). `vmdebootstrap` is a wrapper around it to install Debian into
a disk image, which can be used with a virtual machine (such as KVM).
See the manual page and `vmdebootstrap --help` for details on how to
use the program. The manual page has an example.
Limitations
-----------
`vmdebootstrap` is aimed principally at creating virtual machines, not
installers or prebuilt installation images. It is possible to create
prebuilt installation images for some devices but this depends on the
specific device. (A 'prebuilt installation image' is a single image file
which can be written to physical media in a single operation and which
allows the device to boot directly into a fully installed system - in a
similar way to how a virtual machine would behave.)
* `vmdebootstrap` assumes that all operations take place on a local image
file, not a physical block device / removable media.
* `vmdebootstrap` is intended to be used with tools like `qemu` on the
command line to launch a new virtual machine. Not all devices have
virtualisation support in hardware.
This has implications for `u-boot` support in some cases. If the device
can support reading the bootloader from a known partition, like the
Beaglebone-black, then `vmdebootstrap` can provide space for the bootloader
and the image will work as a prebuilt installation image. If the device
expects that the bootloader exists at a specific offset and therefore
requires that the bootloader is written as an image not as a binary which
can be copied into an existing partition, `vmdebootstrap` is unable to
include that bootloader image into the virtual machine image.
It is possible to wrap `vmdebootstrap` in such a way as to prepare a
*physical block device* with a bootloader image and then deploy the
bootstrap on top. However, this does require physical media to be
inserted and removed each time the wrapper is executed. Once you have
working media, an image can be created using ``dd`` to read back from
the media to an image file, allowing other media to be written with a
single image file. To do this, use the `--tarball` option to `vmdebootstrap`
instead of the `--image`` option. Then setup the physical media and
bootloader image as required for the device, redefine the partitions to
make space for the rootfs, create a filesystem on the physical media and
unpack the `vmdebootstrap` tarball onto that filesystem.
What you need
-------------
In order to use vmdebootstrap, you'll need a few things:
* debootstrap
* extlinux
* qemu-img (in the qemu-utils package in Debian)
* parted
* mbr
* kpartx
* python-cliapp (see http://liw.fi/cliapp/)
The vmextract helper
--------------------
Once the image is built, various files can be generated or modified
during the install operations and some of these files can be useful
when testing the image. One example is the initrd built by the process
of installing a Debian kernel. Rather than having to mount the image
and copy the files manually, the vmextract helper can do it for you,
without needing root privileges.
$ /usr/share/vmdebootstrap/vmextract.py --verbose \
--image bbb/bbb-debian-armmp.img --boot \
--path /boot/initrd.img-3.14-2-armmp \
--path /lib/arm-linux-gnueabihf/libresolv.so.2
This uses python-guestfs (a Recommended package for vmdebootstrap) to
prepare a read-only version of the image - in this case with the /boot
partition also mounted - and copies files out into the current working
directory.
Legalese
--------
Copyright 2011-2013 Lars Wirzenius
Copyright 2012 Codethink Limited
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
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