I’m getting
$ curl https://sh.rustup.rs -sSf | sh
usage: mktemp [-d] [-q] [-t prefix] [-u] template ...
mktemp [-d] [-q] [-u] -t prefix
rustup: command failed: mktemp -d
info: downloading installer
mkdir: : No such file or directory
rustup: command failed: mkdir -p
on OSX 10.10 after uninstalling multirust with
$ curl -sf https://raw.githubusercontent.com/brson/multirust/master/blastoff.sh | sh -s -- --uninstall.