Note that RootStock has been deprecated and is no longer maintained, and it's generally recommended that people start with an ubuntu-core image and tailor it to their needs. If one really needs to build images from the ground up, using live-build is the alternative (which is what Ubuntu uses to generate its own live and preinstalled images, including the ubuntu-core rootfs)
The RootStock project aims to create a command line and graphical set of tools to create a fully configured tarball or VM image of an Ubuntu rootfs from scratch, so that you can extract it to a root device on e.g. armel systems.
Creating a rootfs can help you testing Ubuntu in devices that are not official supported. It also helps you if you want to create smaller images, or just different flavors of Ubuntu (with Gnome, KDE, XFCE, etc).
Project in Launchpad: https://launchpad.net/project-rootstock
July 30, 2010 - RootStock 0.1.99.4 released
RootStock is quite tight with Ubuntu, so we recommend you to use Ubuntu Jaunty, Karmic or Lucid.
Official distro package
Just install rootstock for cli or rootstock-gtk if you want to use the GUI (not well supported).
$ sudo apt-get install rootstock
If you want to use a not yet released version, or want to contribute to RootStock, just pull from the official branch:
$ bzr branch lp:project-rootstock
For older Ubuntu versions you can also use RootStock in order to be able to use the latest features.
Bugs and Problems
If you run into any problem, please report it at https://bugs.launchpad.net/project-rootstock/+filebug .
For questions please contact "ogra" or "rsalveti" in #ubuntu-arm on irc.freenode.net.