I am using emerge --buildpkgonly as a regular user to test packages. I tried this for a package I have enabled debugging, and for that one portage errors out trying to install sources into /usr/src/debug: $ FEATURES=test emerge --buildpkgonly --jobs=1 -av1 clhep [snip] >>> Completed installing sci-physics/clhep-2.4.1.2 into /tmp/portage/sci-physics/clhep-2.4.1.2/image * Final size of build directory: 414268 KiB (404.5 MiB) * Final size of installed tree: 106892 KiB (104.3 MiB) strip: x86_64-pc-linux-gnu-strip --strip-unneeded -N __gentoo_check_ldflags__ -R .comment -R .GCC.command.line -R .note.gnu.gold-version /usr/lib64/libCLHEP-2.4.1.2.a /usr/lib64/libCLHEP-2.4.1.2.so /usr/lib64/libCLHEP-Evaluator-2.4.1.2.so /usr/lib64/libCLHEP-Evaluator-2.4.1.2.a /usr/lib64/libCLHEP-Vector-2.4.1.2.a /usr/lib64/libCLHEP-GenericFunctions-2.4.1.2.a /usr/lib64/libCLHEP-Vector-2.4.1.2.so /usr/lib64/libCLHEP-GenericFunctions-2.4.1.2.so /usr/lib64/libCLHEP-RandomObjects-2.4.1.2.a /usr/lib64/libCLHEP-RandomObjects-2.4.1.2.so /usr/lib64/libCLHEP-Geometry-2.4.1.2.so /usr/lib64/libCLHEP-Geometry-2.4.1.2.a /usr/lib64/libCLHEP-Matrix-2.4.1.2.so /usr/lib64/libCLHEP-Cast-2.4.1.2.so /usr/lib64/libCLHEP-Matrix-2.4.1.2.a /usr/lib64/libCLHEP-Cast-2.4.1.2.a /usr/lib64/libCLHEP-Random-2.4.1.2.so /usr/lib64/libCLHEP-Random-2.4.1.2.a /usr/lib64/libCLHEP-RefCount-2.4.1.2.so /usr/lib64/libCLHEP-RefCount-2.4.1.2.a /usr/lib64/libCLHEP-Exceptions-2.4.1.2.so /usr/lib64/libCLHEP-Exceptions-2.4.1.2.a installsources: rsyncing source files /usr/lib/portage/python3.6/misc-functions.sh: line 467: /var/cache/binpkgs/sci-physics/clhep-2.4.1.2.tbz2.606931: Permission denied ./ ./usr/ ./usr/src/ ./usr/src/debug/ ./usr/src/debug/sci-physics/ ./usr/src/debug/sci-physics/clhep-2.4.1.2/ ./usr/src/debug/sci-physics/clhep-2.4.1.2/clhep-2.4.1.2_build/ I think that when only building the package, portage should not try to install sources into /usr/src/debug.