While taking a look into GCC upgrade guide I notice that I needed to manually check which packages are present on each of my systems to run https://wiki.gentoo.org/wiki/Upgrading_GCC#Which_packages_are_known_to_need_a_rebuild.3F # emerge --ask --oneshot --usepkg=n --verbose sys-devel/libtool sys-devel/llvm sys-devel/clang dev-python/wxpython dev-python/wxGTK only for the relevant packages Maybe it would be interesting to add a --rebuild command that would simply skip the packages that are not present in the system and, implicitly, pass --oneshot too. That way users will simply be able to run something like: # emerge --ask --rebuild --usepkg=n --verbose sys-devel/libtool sys-devel/llvm sys-devel/clang dev-python/wxpython dev-python/wxGTK and it will simply rebuild the packages from that list that are present in the system while skipping the others Thanks a lot