<!-- Thanks for filing a 🐛 bug report 😄! --> **Problem** <!-- A clear and concise description of what the bug is. --> <!-- including what currently happens and what you expected to happen. --> I am using a custom`CARGO_HOME` and when I do `rustup update stable`, I get this error: `error: rustup is not installed at '/Users/lucas/.my-cargo-dir`. **Steps** <!-- The steps to reproduce the bug. --> CARGO_HOME=/tmp/somedir rustup update stable **Possible Solution(s)** <!-- Not obligatory, but suggest a fix/reason for the bug, --> <!-- or ideas how to implement the addition or change --> **Notes** Output of `rustup --version`: rustup 1.21.1 (7832b2ebe 2019-12-20) Output of `rustup show`: Default host: x86_64-apple-darwin rustup home: /Users/lucas/.rustup installed toolchains -------------------- stable-x86_64-apple-darwin nightly-x86_64-apple-darwin installed targets for active toolchain -------------------------------------- wasm32-unknown-unknown x86_64-apple-darwin active toolchain ---------------- stable-x86_64-apple-darwin (default) rustc 1.43.0 (4fb7144ed 2020-04-20)