Perhaps they use Automated Linux from Scratch? http://www.linuxfromscratch.org/alfs/ http://www.linuxfromscratch.org/alfs/ Although there's little documentati

Perhaps they use Automated Linux from Scratch? http://www.linuxfromscratch.org/alfs/ http://www.linuxfromscratch.org/alfs/ Although there's little documentation to speak of, so I can't tell whether it helps with upgrades. If you want to build from source and tinker with compile flags but also be able to upgrade seamlessly, Gentoo or Arch Linux is probably more appropriate.