Stage 1 tarballs are generated from a packages.build file. Each system profile may have a slightly different base.packages file:
Stage 2 tarballs contain the same packages as a stage 1 tarball with one caveat: stage 2 tarballs are compiled from a stage 1 tarball. This is to ensure the stage 1 tarball contains the tool chain necessary to reproduce itself.
Stage 3 tarballs are compiled from stage 2 tarballs, but contain a system set. Portage includes a quick reference to this set of base packages by using the @system set operator.
Not including sub-profiles, the base file used for the system set of all profiles can be found at: /usr/portage/profiles/base/packages
Downloading and decompressing a stage 3 tarball as described in Gentoo handbook will install an almost-complete and almost-functional system (the most important parts still missing are a kernel and a bootloader).
A cloud stage 4 has been created to aid in the process of virtual machine provisioning. These stage 4 files can be used with diskimage-builder (available via app-emulation/diskimage-builder). See the Gentoo README upstream and official diskimage-builder documentation for more information.
- http://www.funtoo.org/Stage_Tarball - Stage tarball explained on the Funtoo Linux wiki.