root@host / $ rustup-init
warning: it looks like you have an existing installation of Rust at:
warning: /usr/bin
warning: It is recommended that rustup be the primary Rust installation.
warning: Otherwise you may have confusion unless you are careful with your PATH
warning: If you are sure that you want both rustup and your already installed Rust
warning: then please reply `y' or `yes' or set RUSTUP_INIT_SKIP_PATH_CHECK to yes
warning: or pass `-y' to ignore all ignorable checks.
error: cannot install while Rust is installed