The IPP nodes all run Gentoo and we have our own small portage overlay to add and/or modify a few .ebuilds.

Our /etc/portage/* configuration files:
[http://svn.pan-starrs.ifa.hawaii.edu/trac/ipp/browser/trunk/portage]

Our portage overlay:
[http://svn.pan-starrs.ifa.hawaii.edu/trac/ipp/browser/trunk/portage_overlay]

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Recommend reading
 * [http://devmanual.gentoo.org/]