That may be a problem with the parallel build. Just try cmake --build . -- -j1 or make -j1 if using the classic build script and it should be able to go to the end. Also, if you are not tied to ROOT 6.10, I recommend you to try v6.11/02, which was recently released and will work fine to build in parallel. It also has many improvements compared with 6.10/06. Cheers,