Cargo Home

The "Cargo home" functions as a download and source cache. When building a crate, Cargo stores downloaded build dependencies in the Cargo home. You can alter the location of the Cargo home by setting the CARGO_HOME environmental variable. The home crate provides an API for getting this location if you need this information inside your Rust crate. By default, the Cargo home is located in $HOME/.cargo/.

Please note that the internal structure of the Cargo home is not stabilized and may be subject to change at any time.

The Cargo home consists of following components:

Files:

Directories:

  • bin The bin directory contains executables of crates that were installed via cargo install or rustup. To be able to make these binaries accessible, add the path of the directory to your $PATH environment variable.

  • git Git sources are stored here:

    • git/db When a crate depends on a git repository, Cargo clones the repo as a bare repo into this directory and updates it if necessary.

    • git/checkouts If a git source is used, the required commit of the repo is checked out from the bare repo inside git/db into this directory. This provides the compiler with the actual files contained in the repo of the commit specified for that dependency. Multiple checkouts of different commits of the same repo are possible.

  • registry Packages and metadata of crate registries (such as crates.io) are located here.

    • registry/index The index is a bare git repository which contains the metadata (versions, dependencies etc) of all available crates of a registry.

    • registry/cache Downloaded dependencies are stored in the cache. The crates are compressed gzip archives named with a .crate extension.

    • registry/src If a downloaded .crate archive is required by a package, it is unpacked into registry/src folder where rustc will find the .rs files.

Caching the Cargo home in CI

To avoid redownloading all crate dependencies during continuous integration, you can cache the $CARGO_HOME directory. However, caching the entire directory is often inefficient as it will contain downloaded sources twice. If we depend on a crate such as serde 1.0.92 and cache the entire $CARGO_HOME we would actually cache the sources twice, the serde-1.0.92.crate inside registry/cache and the extracted .rs files of serde inside registry/src. That can unnecessarily slow down the build as downloading, extracting, recompressing and reuploading the cache to the CI servers can take some time.

It should be sufficient to only cache the following directories across builds:

  • bin/
  • registry/index/
  • registry/cache/
  • git/db/

Vendoring all dependencies of a project

See the cargo vendor subcommand.

Clearing the cache

In theory, you can always remove any part of the cache and Cargo will do its best to restore sources if a crate needs them either by reextracting an archive or checking out a bare repo or by simply redownloading the sources from the web.

Alternatively, the cargo-cache crate provides a simple CLI tool to only clear selected parts of the cache or show sizes of its components in your command-line.