Do you have rights to create a dir at
/usr/local/lib ?
If not rustup.sh won’t be able to install rust there.
It might make sense to have more verbose error messages if rustup.sh doesn’t have the rights to create change the destination directories or the path is missing.
BTW. If I am not wrong this forum is mainly for discussions about rust and it’s future. For future questions of this kind consulting the rust IRC and stack overflow might be preferred.