Rustup has a TOML settings file at ${RUSTUP_HOME}/settings.toml (which defaults to ~/.rustup or %USERPROFILE%/.rustup). The schema for this file is not part of the public interface for rustup - the rustup CLI should be used to query and set settings.

On Unix operating systems a fallback settings file is consulted for some settings. This fallback file is located at /etc/rustup/settings.toml and currently can define only default_toolchain.