"error: Invalid cross-device link (os error 18)" when installing toolchain

[RalfJung]

Calling rustup-toolchain-install-master -c rust-src -- d28a9c38fe14396e86ae274c7847e20ee0f78ca9, I am getting the following output:

detecting the channel of the `d28a9c38fe14396e86ae274c7847e20ee0f78ca9` toolchain...
downloading <https://rust-lang-ci2.s3-us-west-1.amazonaws.com/rustc-builds/d28a9c38fe14396e86ae274c7847e20ee0f78ca9/rustc-nightly-x86_64-unknown-linux-gnu.tar.xz>...
completed                                                                                                                                                                                                                                    downloading <https://rust-lang-ci2.s3-us-west-1.amazonaws.com/rustc-builds/d28a9c38fe14396e86ae274c7847e20ee0f78ca9/rust-src-nightly.tar.xz>...
completed                                                                                                                                                                                                                                    downloading <https://rust-lang-ci2.s3-us-west-1.amazonaws.com/rustc-builds/d28a9c38fe14396e86ae274c7847e20ee0f78ca9/rust-std-nightly-x86_64-unknown-linux-gnu.tar.xz>...
completed                                                                                                                                                                                                                                    

error: Invalid cross-device link (os error 18)

I've seen this error before but only briefly (it went away, not sure what caused that), now it seems to stick unfortunately.

Looks like this is #3 having come back.

$ rustup-toolchain-install-master --version
rustup-toolchain-install-master 1.7.0