Ответ на твой вопрос есть в man 5 portage ближе к концу.

Спасибо

/var/db/pkg/
All installed package information is recorded here. If portage
thinks you have a package installed, it is usually because it is
listed here.

The format follows somewhat closely that of the portage tree.
There is a directory for each category and a package-version
subdirectory for each package you have installed.

Inside each package directory are misc files that describe the
installed contents of the package as well as build time informa-
tion (so that the package can be unmerged without needing the
portage tree).

The exact file contents and format are not described here again
so that things can be changed quickly. Generally though there
is one file per environment variable that "matters" (like
CFLAGS) with the contents stored inside of it. Another common
file is the CONTENTS file which lists the path and hashes of all
objects that the package installed onto your system.