In the Handbook's section "Working with Portage", in the subsection "Diverting from the official tree", overlays are explained. A far as i know, there's a gentoo official way to sync overlay repositories and that's gensync from gentoolkit-dev. That utility should be at least mentioned, if not briefly explained.
CCing karltk for his opinion(s) on this. Is gensync stable enough to go into the handbook? Karl, any chances of a patch for this? Since you've written the man page..thought you'll be the best person to know/ask. TIA
Okay, gensync is now mentioned in the guide. But remember, gensync doesn't do much except synchronise overlays. The real workhorse here is still Portage (iow, you don't need gensync to update repositories).
