Configuration - The Cargo Book

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# Configuration

This document explains how Cargo’s configuration system works, as well as available keys or configuration. For configuration of a package through its manifest, see the manifest format.

## Hierarchical structure

Cargo allows local configuration for a particular package as well as global configuration. It looks for configuration files in the current directory and all parent directories. If, for example, Cargo were invoked in `/projects/foo/bar/baz`, then the following configuration files would be probed for and unified in this order:

- `/projects/foo/bar/baz/.cargo/config.toml`
- `/projects/foo/bar/.cargo/config.toml`
- `/projects/foo/.cargo/config.toml`
- `/projects/.cargo/config.toml`
- `/.cargo/config.toml`
- `$CARGO_HOME/config.toml` which defaults to:
  - Windows: `%USERPROFILE%\.cargo\config.toml`
  - Unix: `$HOME/.cargo/config.toml`

With this structure, you can specify configuration per-package, and even possibly check it into version control. You can also specify personal defaults with a configuration file in your home directory.

If a key is specified in multiple config files, the values will get merged together. Numbers, strings, and booleans will use the value in the deeper config directory taking precedence over ancestor directories, where the home directory is the lowest priority. Arrays will be joined together with higher precedence items being placed later in the merged array.

At present, when being invoked from a workspace, Cargo does not read config files from crates within the workspace. i.e. if a workspace has two crates in it, named `/projects/foo/bar/baz/mylib` and `/projects/foo/bar/baz/mybin`, and there are Cargo configs at `/projects/foo/bar/baz/mylib/.cargo/config.toml` and `/projects/foo/bar/baz/mybin/.cargo/config.toml`, Cargo does not read those configuration files if it is invoked from the workspace root (`/projects/foo/bar/baz/`).

> Note: Cargo also reads config files without the `.toml` extension, such as `.cargo/config`. Support for the `.toml` extension was added in version 1.39 and is the preferred form. If both files exist, Cargo will use the file without the extension.

## Configuration format

Configuration files are written in the TOML format (like the manifest), with simple key-value pairs inside of sections (tables). The following is a quick overview of all settings, with detailed descriptions found below.

    paths = ["/path/to/override"] # path dependency overrides

    [alias]     # command aliases
    b = "build"
    c = "check"
    t = "test"
    r = "run"
    rr = "run --release"
    recursive_example = "rr --example recursions"
    space_example = ["run", "--release", "--", "\"command list\""]

    [build]
    jobs = 1                      # number of parallel jobs, defaults to # of CPUs
    rustc = "rustc"               # the rust compiler tool
    rustc-wrapper = "…"           # run this wrapper instead of `rustc`
    rustc-workspace-wrapper = "…" # run this wrapper instead of `rustc` for workspace members
    rustdoc = "rustdoc"           # the doc generator tool
    target = "triple"             # build for the target triple (ignored by `cargo install`)
    target-dir = "target"         # path of where to place generated artifacts
    build-dir = "target"          # path of where to place intermediate build artifacts
    rustflags = ["…", "…"]        # custom flags to pass to all compiler invocations
    rustdocflags = ["…", "…"]     # custom flags to pass to rustdoc
    incremental = true            # whether or not to enable incremental compilation
    dep-info-basedir = "…"        # path for the base directory for targets in depfiles

    [credential-alias]
    # Provides a way to define aliases for credential providers.
    my-alias = ["/usr/bin/cargo-credential-example", "--argument", "value", "--flag"]

    [doc]
    browser = "chromium"          # browser to use with `cargo doc --open`,
                                  # overrides the `BROWSER` environment variable

    [env]
    # Set ENV_VAR_NAME=value for any process run by Cargo
    ENV_VAR_NAME = "value"
    # Set even if already present in environment
    ENV_VAR_NAME_2 = { value = "value", force = true }
    # `value` is relative to the parent of `.cargo/config.toml`, env var will be the full absolute path
    ENV_VAR_NAME_3 = { value = "relative/path", relative = true }

    [future-incompat-report]
    frequency = 'always' # when to display a notification about a future incompat report

    [cache]
    auto-clean-frequency = "1 day"   # How often to perform automatic cache cleaning

    [cargo-new]
    vcs = "none"              # VCS to use ('git', 'hg', 'pijul', 'fossil', 'none')

    [http]
    debug = false               # HTTP debugging
    proxy = "host:port"         # HTTP proxy in libcurl format
    ssl-version = "tlsv1.3"     # TLS version to use
    ssl-version.max = "tlsv1.3" # maximum TLS version
    ssl-version.min = "tlsv1.1" # minimum TLS version
    timeout = 30                # timeout for each HTTP request, in seconds
    low-speed-limit = 10        # network timeout threshold (bytes/sec)
    cainfo = "cert.pem"         # path to Certificate Authority (CA) bundle
    proxy-cainfo = "cert.pem"   # path to proxy Certificate Authority (CA) bundle
    check-revoke = true         # check for SSL certificate revocation
    multiplexing = true         # HTTP/2 multiplexing
    user-agent = "…"            # the user-agent header

    [install]
    root = "/some/path"         # `cargo install` destination directory

    [net]
    retry = 3                   # network retries
    git-fetch-with-cli = true   # use the `git` executable for git operations
    offline = true              # do not access the network

    [net.ssh]
    known-hosts = ["..."]       # known SSH host keys

    [patch.<registry>]
    # Same keys as for [patch] in Cargo.toml

    [profile.<name>]         # Modify profile settings via config.
    inherits = "dev"         # Inherits settings from [profile.dev].
    opt-level = 0            # Optimization level.
    debug = true             # Include debug info.
    split-debuginfo = '...'  # Debug info splitting behavior.
    strip = "none"           # Removes symbols or debuginfo.
    debug-assertions = true  # Enables debug assertions.
    overflow-checks = true   # Enables runtime integer overflow checks.
    lto = false              # Sets link-time optimization.
    panic = 'unwind'         # The panic strategy.
    incremental = true       # Incremental compilation.
    codegen-units = 16       # Number of code generation units.
    rpath = false            # Sets the rpath linking option.
    [profile.<name>.build-override]  # Overrides build-script settings.
    # Same keys for a normal profile.
    [profile.<name>.package.<name>]  # Override profile for a package.
    # Same keys for a normal profile (minus `panic`, `lto`, and `rpath`).

    [resolver]
    incompatible-rust-versions = "allow"  # Specifies how resolver reacts to these

    [registries.<name>]  # registries other than crates.io
    index = "…"          # URL of the registry index
    token = "…"          # authentication token for the registry
    credential-provider = "cargo:token" # The credential provider for this registry.

    [registries.crates-io]
    protocol = "sparse"  # The protocol to use to access crates.io.

    [registry]
    default = "…"        # name of the default registry
    token = "…"          # authentication token for crates.io
    credential-provider = "cargo:token"           # The credential provider for crates.io.
    global-credential-providers = ["cargo:token"] # The credential providers to use by default.

    [source.<name>]      # source definition and replacement
    replace-with = "…"   # replace this source with the given named source
    directory = "…"      # path to a directory source
    registry = "…"       # URL to a registry source
    local-registry = "…" # path to a local registry source
    git = "…"            # URL of a git repository source
    branch = "…"         # branch name for the git repository
    tag = "…"            # tag name for the git repository
    rev = "…"            # revision for the git repository

    [target.<triple>]
    linker = "…"              # linker to use
    runner = "…"              # wrapper to run executables
    rustflags = ["…", "…"]    # custom flags for `rustc`
    rustdocflags = ["…", "…"] # custom flags for `rustdoc`

    [target.<cfg>]
    linker = "…"            # linker to use
    runner = "…"            # wrapper to run executables
    rustflags = ["…", "…"]  # custom flags for `rustc`

    [target.<triple>.<links>] # `links` build script override
    rustc-link-lib = ["foo"]
    rustc-link-search = ["/path/to/foo"]
    rustc-flags = "-L /some/path"
    rustc-cfg = ['key="value"']
    rustc-env = {key = "value"}
    rustc-cdylib-link-arg = ["…"]
    metadata_key1 = "value"
    metadata_key2 = "value"

    [term]
    quiet = false                    # whether cargo output is quiet
    verbose = false                  # whether cargo provides verbose output
    color = 'auto'                   # whether cargo colorizes output
    hyperlinks = true                # whether cargo inserts links into output
    unicode = true                   # whether cargo can render output using non-ASCII unicode characters
    progress.when = 'auto'           # whether cargo shows progress bar
    progress.width = 80              # width of progress bar
    progress.term-integration = true # whether cargo reports progress to terminal emulator

## Environment variables

Cargo can also be configured through environment variables in addition to the TOML configuration files. For each configuration key of the form `foo.bar` the environment variable `CARGO_FOO_BAR` can also be used to define the value. Keys are converted to uppercase, dots and dashes are converted to underscores. For example the `target.x86_64-unknown-linux-gnu.runner` key can also be defined by the `CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER` environment variable.

Environment variables will take precedence over TOML configuration files. Currently only integer, boolean, string and some array values are supported to be defined by environment variables. Descriptions below indicate which keys support environment variables and otherwise they are not supported due to technical issues.

In addition to the system above, Cargo recognizes a few other specific environment variables.

## Command-line overrides

Cargo also accepts arbitrary configuration overrides through the `--config` command-line option. The argument should be in TOML syntax of `KEY=VALUE` or provided as a path to an extra configuration file:

    # With `KEY=VALUE` in TOML syntax
    cargo --config net.git-fetch-with-cli=true fetch

    # With a path to a configuration file
    cargo --config ./path/to/my/extra-config.toml fetch

The `--config` option may be specified multiple times, in which case the values are merged in left-to-right order, using the same merging logic that is used when multiple configuration files apply. Configuration values specified this way take precedence over environment variables, which take precedence over configuration files.

When the `--config` option is provided as an extra configuration file, The configuration file loaded this way follow the same precedence rules as other options specified directly with `--config`.

Some examples of what it looks like using Bourne shell syntax:

    # Most shells will require escaping.
    cargo --config http.proxy=\"http://example.com\" …

    # Spaces may be used.
    cargo --config "net.git-fetch-with-cli = true" …

    # TOML array example. Single quotes make it easier to read and write.
    cargo --config 'build.rustdocflags = ["--html-in-header", "header.html"]' …

    # Example of a complex TOML key.
    cargo --config "target.'cfg(all(target_arch = \"arm\", target_os = \"none\"))'.runner = 'my-runner'" …

    # Example of overriding a profile setting.
    cargo --config profile.dev.package.image.opt-level=3 …

## Config-relative paths

Paths in config files may be absolute, relative, or a bare name without any path separators. Paths for executables without a path separator will use the `PATH` environment variable to search for the executable. Paths for non-executables will be relative to where the config value is defined.

In particular, rules are:

- For environment variables, paths are relative to the current working directory.
- For config values loaded directly from the `--config KEY=VALUE` option, paths are relative to the current working directory.
- For config files, paths are relative to the parent directory of the directory where the config files were defined, no matter those files are from either the hierarchical probing or the `--config <path>` option.

> Note: To maintain consistency with existing `.cargo/config.toml` probing behavior, it is by design that a path in a config file passed via `--config <path>` is also relative to two levels up from the config file itself.

> To avoid unexpected results, the rule of thumb is putting your extra config files at the same level of discovered `.cargo/config.toml` in your project. For instance, given a project `/my/project`, it is recommended to put config files under `/my/project/.cargo` or a new directory at the same level, such as `/my/project/.config`.

    # Relative path examples.

    [target.x86_64-unknown-linux-gnu]
    runner = "foo"  # Searches `PATH` for `foo`.

    [source.vendored-sources]
    # Directory is relative to the parent where `.cargo/config.toml` is located.
    # For example, `/my/project/.cargo/config.toml` would result in `/my/project/vendor`.
    directory = "vendor"

## Executable paths with arguments

Some Cargo commands invoke external programs, which can be configured as a path and some number of arguments.

The value may be an array of strings like `['/path/to/program', 'somearg']` or a space-separated string like `'/path/to/program somearg'`. If the path to the executable contains a space, the list form must be used.

If Cargo is passing other arguments to the program such as a path to open or run, they will be passed after the last specified argument in the value of an option of this format. If the specified program does not have path separators, Cargo will search `PATH` for its executable.

## Credentials

Configuration values with sensitive information are stored in the `$CARGO_HOME/credentials.toml` file. This file is automatically created and updated by `cargo login` and `cargo logout` when using the `cargo:token` credential provider.

Tokens are used by some Cargo commands such as `cargo publish` for authenticating with remote registries. Care should be taken to protect the tokens and to keep them secret.

It follows the same format as Cargo config files.

    [registry]
    token = "…"   # Access token for crates.io

    [registries.<name>]
    token = "…"   # Access token for the named registry

As with most other config values, tokens may be specified with environment variables. The token for crates.io may be specified with the `CARGO_REGISTRY_TOKEN` environment variable. Tokens for other registries may be specified with environment variables of the form `CARGO_REGISTRIES_<name>_TOKEN` where `<name>` is the name of the registry in all capital letters.

> Note: Cargo also reads and writes credential files without the `.toml` extension, such as `.cargo/credentials`. Support for the `.toml` extension was added in version 1.39. In version 1.68, Cargo writes to the file with the extension by default. However, for backward compatibility reason, when both files exist, Cargo will read and write the file without the extension.

## Configuration keys

This section documents all configuration keys. The description for keys with variable parts are annotated with angled brackets like `target.<triple>` where the `<triple>` part can be any target triple like `target.x86_64-pc-windows-msvc`.

### `paths`

- Type: array of strings (paths)
- Default: none
- Environment: not supported

An array of paths to local packages which are to be used as overrides for dependencies. For more information see the Overriding Dependencies guide.

### `[alias]`

- Type: string or array of strings
- Default: see below
- Environment: `CARGO_ALIAS_<name>`

The `[alias]` table defines CLI command aliases. For example, running `cargo b` is an alias for running `cargo build`. Each key in the table is the subcommand, and the value is the actual command to run. The value may be an array of strings, where the first element is the command and the following are arguments. It may also be a string, which will be split on spaces into subcommand and arguments. The following aliases are built-in to Cargo:

    [alias]
    b = "build"
    c = "check"
    d = "doc"
    t = "test"
    r = "run"
    rm = "remove"

Aliases are not allowed to redefine existing built-in commands.

Aliases are recursive:

    [alias]
    rr = "run --release"
    recursive_example = "rr --example recursions"

### `[build]`

The `[build]` table controls build-time operations and compiler settings.

#### `build.jobs`

- Type: integer or string
- Default: number of logical CPUs
- Environment: `CARGO_BUILD_JOBS`

Sets the maximum number of compiler processes to run in parallel. If negative, it sets the maximum number of compiler processes to the number of logical CPUs plus provided value. Should not be 0. If a string `default` is provided, it sets the value back to defaults.

Can be overridden with the `--jobs` CLI option.

#### `build.rustc`

- Type: string (program path)
- Default: `"rustc"`
- Environment: `CARGO_BUILD_RUSTC` or `RUSTC`

Sets the executable to use for `rustc`.

#### `build.rustc-wrapper`

- Type: string (program path)
- Default: none
- Environment: `CARGO_BUILD_RUSTC_WRAPPER` or `RUSTC_WRAPPER`

Sets a wrapper to execute instead of `rustc`. The first argument passed to the wrapper is the path to the actual executable to use (i.e., `build.rustc`, if that is set, or `"rustc"` otherwise).

#### `build.rustc-workspace-wrapper`

- Type: string (program path)
- Default: none
- Environment: `CARGO_BUILD_RUSTC_WORKSPACE_WRAPPER` or `RUSTC_WORKSPACE_WRAPPER`

Sets a wrapper to execute instead of `rustc`, for workspace members only. When building a single-package project without workspaces, that package is considered to be the workspace. The first argument passed to the wrapper is the path to the actual executable to use (i.e., `build.rustc`, if that is set, or `"rustc"` otherwise). It affects the filename hash so that artifacts produced by the wrapper are cached separately.

If both `rustc-wrapper` and `rustc-workspace-wrapper` are set, then they will be nested: the final invocation is `$RUSTC_WRAPPER $RUSTC_WORKSPACE_WRAPPER $RUSTC`.

#### `build.rustdoc`

- Type: string (program path)
- Default: `"rustdoc"`
- Environment: `CARGO_BUILD_RUSTDOC` or `RUSTDOC`

Sets the executable to use for `rustdoc`.

#### `build.target`

- Type: string or array of strings
- Default: host platform
- Environment: `CARGO_BUILD_TARGET`

The default target platform triples to compile to.

Possible values:

- Any supported target in `rustc --print target-list`.
- `"host-tuple"`, which will internally be substituted by the host’s target. This can be particularly useful if you’re cross-compiling some crates, and don’t want to specify your host’s machine as a target (for instance, an `xtask` in a shared project that may be worked on by many hosts).
- A path to a custom target specification. See Custom Target Lookup Path for more information.

Can be overridden with the `--target` CLI option.

    [build]
    target = ["x86_64-unknown-linux-gnu", "i686-unknown-linux-gnu"]

#### `build.target-dir`

- Type: string (path)
- Default: `"target"`
- Environment: `CARGO_BUILD_TARGET_DIR` or `CARGO_TARGET_DIR`

The path to where all compiler output is placed. The default if not specified is a directory named `target` located at the root of the workspace.

Can be overridden with the `--target-dir` CLI option.

For more information see the build cache documentation.

#### `build.build-dir`

- Type: string (path)
- Default: Defaults to the value of `build.target-dir`
- Environment: `CARGO_BUILD_BUILD_DIR`

The directory where intermediate build artifacts will be stored. Intermediate artifacts are produced by Rustc/Cargo during the build process.

This option supports path templating.

Available template variables:

- `{workspace-root}` resolves to root of the current workspace.
- `{cargo-cache-home}` resolves to `CARGO_HOME`
- `{workspace-path-hash}` resolves to a hash of the manifest path

For more information see the build cache documentation.

#### `build.rustflags`

- Type: string or array of strings
- Default: none
- Environment: `CARGO_BUILD_RUSTFLAGS` or `CARGO_ENCODED_RUSTFLAGS` or `RUSTFLAGS`

Extra command-line flags to pass to `rustc`. The value may be an array of strings or a space-separated string.

There are four mutually exclusive sources of extra flags. They are checked in order, with the first one being used:

1. `CARGO_ENCODED_RUSTFLAGS` environment variable.
2. `RUSTFLAGS` environment variable.
3. All matching `target.<triple>.rustflags` and `target.<cfg>.rustflags` config entries joined together.
4. `build.rustflags` config value.

Additional flags may also be passed with the `cargo rustc` command.

If the `--target` flag (or `build.target`) is used, then the flags will only be passed to the compiler for the target. Things being built for the host, such as build scripts or proc macros, will not receive the args. Without `--target`, the flags will be passed to all compiler invocations (including build scripts and proc macros) because dependencies are shared. If you have args that you do not want to pass to build scripts or proc macros and are building for the host, pass `--target` with the host triple.

It is not recommended to pass in flags that Cargo itself usually manages. For example, the flags driven by profiles are best handled by setting the appropriate profile setting.

> Caution: Due to the low-level nature of passing flags directly to the compiler, this may cause a conflict with future versions of Cargo which may issue the same or similar flags on its own which may interfere with the flags you specify. This is an area where Cargo may not always be backwards compatible.

#### `build.rustdocflags`

- Type: string or array of strings
- Default: none
- Environment: `CARGO_BUILD_RUSTDOCFLAGS` or `CARGO_ENCODED_RUSTDOCFLAGS` or `RUSTDOCFLAGS`

Extra command-line flags to pass to `rustdoc`. The value may be an array of strings or a space-separated string.

There are four mutually exclusive sources of extra flags. They are checked in order, with the first one being used:

1. `CARGO_ENCODED_RUSTDOCFLAGS` environment variable.
2. `RUSTDOCFLAGS` environment variable.
3. All matching `target.<triple>.rustdocflags` config entries joined together.
4. `build.rustdocflags` config value.

Additional flags may also be passed with the `cargo rustdoc` command.

> Caution: Due to the low-level nature of passing flags directly to the compiler, this may cause a conflict with future versions of Cargo which may issue the same or similar flags on its own which may interfere with the flags you specify. This is an area where Cargo may not always be backwards compatible.

#### `build.incremental`

- Type: bool
- Default: from profile
- Environment: `CARGO_BUILD_INCREMENTAL` or `CARGO_INCREMENTAL`

Whether or not to perform incremental compilation. The default if not set is to use the value from the profile. Otherwise this overrides the setting of all profiles.

The `CARGO_INCREMENTAL` environment variable can be set to `1` to force enable incremental compilation for all profiles, or `0` to disable it. This env var overrides the config setting.

#### `build.dep-info-basedir`

- Type: string (path)
- Default: none
- Environment: `CARGO_BUILD_DEP_INFO_BASEDIR`

Strips the given path prefix from dep info file paths. This config setting is intended to convert absolute paths to relative paths for tools that require relative paths.

The setting itself is a config-relative path. So, for example, a value of `"."` would strip all paths starting with the parent directory of the `.cargo` directory.

#### `build.pipelining`

This option is deprecated and unused. Cargo always has pipelining enabled.

### `[credential-alias]`

- Type: string or array of strings
- Default: empty
- Environment: `CARGO_CREDENTIAL_ALIAS_<name>`

The `[credential-alias]` table defines credential provider aliases. These aliases can be referenced as an element of the `registry.global-credential-providers` array, or as a credential provider for a specific registry under `registries.<NAME>.credential-provider`.

If specified as a string, the value will be split on spaces into path and arguments.

For example, to define an alias called `my-alias`:

    [credential-alias]
    my-alias = ["/usr/bin/cargo-credential-example", "--argument", "value", "--flag"]

See Registry Authentication for more information.

### `[doc]`

The `[doc]` table defines options for the `cargo doc` command.

#### `doc.browser`

- Type: string or array of strings (program path with args)
- Default: `BROWSER` environment variable, or, if that is missing, opening the link in a system specific way

This option sets the browser to be used by `cargo doc`, overriding the `BROWSER` environment variable when opening documentation with the `--open` option.

### `[cargo-new]`

The `[cargo-new]` table defines defaults for the `cargo new` command.

#### `cargo-new.name`

This option is deprecated and unused.

#### `cargo-new.email`

This option is deprecated and unused.

#### `cargo-new.vcs`

- Type: string
- Default: `"git"` or `"none"`
- Environment: `CARGO_CARGO_NEW_VCS`

Specifies the source control system to use for initializing a new repository. Valid values are `git`, `hg` (for Mercurial), `pijul`, `fossil` or `none` to disable this behavior. Defaults to `git`, or `none` if already inside a VCS repository. Can be overridden with the `--vcs` CLI option.

### `[env]`

The `[env]` section allows you to set additional environment variables for build scripts, rustc invocations, `cargo run` and `cargo build`.

    [env]
    OPENSSL_DIR = "/opt/openssl"

By default, the variables specified will not override values that already exist in the environment. This behavior can be changed by setting the `force` flag.

Setting the `relative` flag evaluates the value as a config-relative path that is relative to the parent directory of the `.cargo` directory that contains the `config.toml` file. The value of the environment variable will be the full absolute path.

    [env]
    TMPDIR = { value = "/home/tmp", force = true }
    OPENSSL_DIR = { value = "vendor/openssl", relative = true }

### `[future-incompat-report]`

The `[future-incompat-report]` table controls setting for future incompat reporting

#### `future-incompat-report.frequency`

- Type: string
- Default: `"always"`
- Environment: `CARGO_FUTURE_INCOMPAT_REPORT_FREQUENCY`

Controls how often we display a notification to the terminal when a future incompat report is available. Possible values:

- `always` (default): Always display a notification when a command (e.g. `cargo build`) produces a future incompat report
- `never`: Never display a notification

### `[cache]`

The `[cache]` table defines settings for cargo’s caches.

#### Global caches

When running `cargo` commands, Cargo will automatically track which files you are using within the global cache. Periodically, Cargo will delete files that have not been used for some period of time. It will delete files that have to be downloaded from the network if they have not been used in 3 months. Files that can be generated without network access will be deleted if they have not been used in 1 month.

The automatic deletion of files only occurs when running commands that are already doing a significant amount of work, such as all of the build commands (`cargo build`, `cargo test`, `cargo check`, etc.), and `cargo fetch`.

Automatic deletion is disabled if cargo is offline such as with `--offline` or `--frozen` to avoid deleting artifacts that may need to be used if you are offline for a long period of time.

> Note: This tracking is currently only implemented for the global cache in Cargo’s home directory. This includes registry indexes and source files downloaded from registries and git dependencies. Support for tracking build artifacts is not yet implemented, and tracked in cargo#13136.

> Additionally, there is an unstable feature to support manually triggering cache cleaning, and to further customize the configuration options. See the Unstable chapter for more information.

#### `cache.auto-clean-frequency`

- Type: string
- Default: `"1 day"`
- Environment: `CARGO_CACHE_AUTO_CLEAN_FREQUENCY`

This option defines how often Cargo will automatically delete unused files in the global cache. This does not define how old the files must be, those thresholds are described above.

It supports the following settings:

- `"never"` — Never deletes old files.
- `"always"` — Checks to delete old files every time Cargo runs.
- An integer followed by “seconds”, “minutes”, “hours”, “days”, “weeks”, or “months” — Checks to delete old files at most the given time frame.

### `[http]`

The `[http]` table defines settings for HTTP behavior. This includes fetching crate dependencies and accessing remote git repositories.

#### `http.debug`

- Type: boolean
- Default: false
- Environment: `CARGO_HTTP_DEBUG`

If `true`, enables debugging of HTTP requests. The debug information can be seen by setting the `CARGO_LOG=network=debug` environment variable (or use `network=trace` for even more information).

Be wary when posting logs from this output in a public location. The output may include headers with authentication tokens which you don’t want to leak! Be sure to review logs before posting them.

#### `http.proxy`

- Type: string
- Default: none
- Environment: `CARGO_HTTP_PROXY` or `HTTPS_PROXY` or `https_proxy` or `http_proxy`

Sets an HTTP and HTTPS proxy to use. The format is in libcurl format as in `[protocol://]host[:port]`. If not set, Cargo will also check the `http.proxy` setting in your global git configuration. If none of those are set, the `HTTPS_PROXY` or `https_proxy` environment variables set the proxy for HTTPS requests, and `http_proxy` sets it for HTTP requests.

#### `http.timeout`

- Type: integer
- Default: 30
- Environment: `CARGO_HTTP_TIMEOUT` or `HTTP_TIMEOUT`

Sets the timeout for each HTTP request, in seconds.

#### `http.cainfo`

- Type: string (path)
- Default: none
- Environment: `CARGO_HTTP_CAINFO`

Path to a Certificate Authority (CA) bundle file, used to verify TLS certificates. If not specified, Cargo attempts to use the system certificates.

#### `http.proxy-cainfo`

- Type: string (path)
- Default: falls back to `http.cainfo` if not set
- Environment: `CARGO_HTTP_PROXY_CAINFO`

Path to a Certificate Authority (CA) bundle file, used to verify proxy TLS certificates.

#### `http.check-revoke`

- Type: boolean
- Default: true (Windows) false (all others)
- Environment: `CARGO_HTTP_CHECK_REVOKE`

This determines whether or not TLS certificate revocation checks should be performed. This only works on Windows.

#### `http.ssl-version`

- Type: string or min/max table
- Default: none
- Environment: `CARGO_HTTP_SSL_VERSION`

This sets the minimum TLS version to use. It takes a string, with one of the possible values of `"default"`, `"tlsv1"`, `"tlsv1.0"`, `"tlsv1.1"`, `"tlsv1.2"`, or `"tlsv1.3"`.

This may alternatively take a table with two keys, `min` and `max`, which each take a string value of the same kind that specifies the minimum and maximum range of TLS versions to use.

The default is a minimum version of `"tlsv1.0"` and a max of the newest version supported on your platform, typically `"tlsv1.3"`.

#### `http.low-speed-limit`

- Type: integer
- Default: 10
- Environment: `CARGO_HTTP_LOW_SPEED_LIMIT`

This setting controls timeout behavior for slow connections. If the average transfer speed in bytes per second is below the given value for `http.timeout` seconds (default 30 seconds), then the connection is considered too slow and Cargo will abort and retry.

#### `http.multiplexing`

- Type: boolean
- Default: true
- Environment: `CARGO_HTTP_MULTIPLEXING`

When `true`, Cargo will attempt to use the HTTP2 protocol with multiplexing. This allows multiple requests to use the same connection, usually improving performance when fetching multiple files. If `false`, Cargo will use HTTP 1.1 without pipelining.

#### `http.user-agent`

- Type: string
- Default: Cargo’s version
- Environment: `CARGO_HTTP_USER_AGENT`

Specifies a custom user-agent header to use. The default if not specified is a string that includes Cargo’s version.

### `[install]`

The `[install]` table defines defaults for the `cargo install` command.

#### `install.root`

- Type: string (path)
- Default: Cargo’s home directory
- Environment: `CARGO_INSTALL_ROOT`

Sets the path to the root directory for installing executables for `cargo install`. Executables go into a `bin` directory underneath the root.

To track information of installed executables, some extra files, such as `.crates.toml` and `.crates2.json`, are also created under this root.

The default if not specified is Cargo’s home directory (default `.cargo` in your home directory).

Can be overridden with the `--root` command-line option.

### `[net]`

The `[net]` table controls networking configuration.

#### `net.retry`

- Type: integer
- Default: 3
- Environment: `CARGO_NET_RETRY`

Number of times to retry possibly spurious network errors.

#### `net.git-fetch-with-cli`

- Type: boolean
- Default: false
- Environment: `CARGO_NET_GIT_FETCH_WITH_CLI`

If this is `true`, then Cargo will use the `git` executable to fetch registry indexes and git dependencies. If `false`, then it uses a built-in `git` library.

Setting this to `true` can be helpful if you have special authentication requirements that Cargo does not support. See Git Authentication for more information about setting up git authentication.

#### `net.offline`

- Type: boolean
- Default: false
- Environment: `CARGO_NET_OFFLINE`

If this is `true`, then Cargo will avoid accessing the network, and attempt to proceed with locally cached data. If `false`, Cargo will access the network as needed, and generate an error if it encounters a network error.

Can be overridden with the `--offline` command-line option.

#### `net.ssh`

The `[net.ssh]` table contains settings for SSH connections.

#### `net.ssh.known-hosts`

- Type: array of strings
- Default: see description
- Environment: not supported

The `known-hosts` array contains a list of SSH host keys that should be accepted as valid when connecting to an SSH server (such as for SSH git dependencies). Each entry should be a string in a format similar to OpenSSH `known_hosts` files. Each string should start with one or more hostnames separated by commas, a space, the key type name, a space, and the base64-encoded key. For example:

    [net.ssh]
    known-hosts = [
        "example.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFO4Q5T0UV0SQevair9PFwoxY9dl4pQl3u5phoqJH3cF"
    ]

Cargo will attempt to load known hosts keys from common locations supported in OpenSSH, and will join those with any listed in a Cargo configuration file. If any matching entry has the correct key, the connection will be allowed.

Cargo comes with the host keys for github.com built-in. If those ever change, you can add the new keys to the config or known_hosts file.

See Git Authentication for more details.

### `[patch]`

Just as you can override dependencies using `[patch]` in `Cargo.toml`, you can override them in the cargo configuration file to apply those patches to any affected build. The format is identical to the one used in `Cargo.toml`.

Since `.cargo/config.toml` files are not usually checked into source control, you should prefer patching using `Cargo.toml` where possible to ensure that other developers can compile your crate in their own environments. Patching through cargo configuration files is generally only appropriate when the patch section is automatically generated by an external build tool.

If a given dependency is patched both in a cargo configuration file and a `Cargo.toml` file, the patch in the configuration file is used. If multiple configuration files patch the same dependency, standard cargo configuration merging is used, which prefers the value defined closest to the current directory, with `$HOME/.cargo/config.toml` taking the lowest precedence.

Relative `path` dependencies in such a `[patch]` section are resolved relative to the configuration file they appear in.

### `[profile]`

The `[profile]` table can be used to globally change profile settings, and override settings specified in `Cargo.toml`. It has the same syntax and options as profiles specified in `Cargo.toml`. See the Profiles chapter for details about the options.

#### `[profile.<name>.build-override]`

- Environment: `CARGO_PROFILE_<name>_BUILD_OVERRIDE_<key>`

The build-override table overrides settings for build scripts, proc macros, and their dependencies. It has the same keys as a normal profile. See the overrides section for more details.

#### `[profile.<name>.package.<name>]`

- Environment: not supported

The package table overrides settings for specific packages. It has the same keys as a normal profile, minus the `panic`, `lto`, and `rpath` settings. See the overrides section for more details.

#### `profile.<name>.codegen-units`

- Type: integer
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_CODEGEN_UNITS`

See codegen-units.

#### `profile.<name>.debug`

- Type: integer or boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_DEBUG`

See debug.

#### `profile.<name>.split-debuginfo`

- Type: string
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_SPLIT_DEBUGINFO`

See split-debuginfo.

#### `profile.<name>.debug-assertions`

- Type: boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_DEBUG_ASSERTIONS`

See debug-assertions.

#### `profile.<name>.incremental`

- Type: boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_INCREMENTAL`

See incremental.

#### `profile.<name>.lto`

- Type: string or boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_LTO`

See lto.

#### `profile.<name>.overflow-checks`

- Type: boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_OVERFLOW_CHECKS`

See overflow-checks.

#### `profile.<name>.opt-level`

- Type: integer or string
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_OPT_LEVEL`

See opt-level.

#### `profile.<name>.panic`

- Type: string
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_PANIC`

See panic.

#### `profile.<name>.rpath`

- Type: boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_RPATH`

See rpath.

#### `profile.<name>.strip`

- Type: string or boolean
- Default: See profile docs.
- Environment: `CARGO_PROFILE_<name>_STRIP`

See strip.

### `[resolver]`

The `[resolver]` table overrides dependency resolution behavior for local development (e.g. excludes `cargo install`).

#### `resolver.incompatible-rust-versions`

- Type: string
- Default: See `resolver` docs
- Environment: `CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS`

When resolving which version of a dependency to use, select how versions with incompatible `package.rust-version`s are treated. Values include:

- `allow`: treat `rust-version`-incompatible versions like any other version
- `fallback`: only consider `rust-version`-incompatible versions if no other version matched

Can be overridden with

- `--ignore-rust-version` CLI option
- Setting the dependency’s version requirement higher than any version with a compatible `rust-version`
- Specifying the version to `cargo update` with `--precise`

See the resolver chapter for more details.

> MSRV:

> - `allow` is supported on any version
> - `fallback` is respected as of 1.84

### `[registries]`

The `[registries]` table is used for specifying additional registries. It consists of a sub-table for each named registry.

#### `registries.<name>.index`

- Type: string (url)
- Default: none
- Environment: `CARGO_REGISTRIES_<name>_INDEX`

Specifies the URL of the index for the registry.

#### `registries.<name>.token`

- Type: string
- Default: none
- Environment: `CARGO_REGISTRIES_<name>_TOKEN`

Specifies the authentication token for the given registry. This value should only appear in the credentials file. This is used for registry commands like `cargo publish` that require authentication.

Can be overridden with the `--token` command-line option.

#### `registries.<name>.credential-provider`

- Type: string or array of path and arguments
- Default: none
- Environment: `CARGO_REGISTRIES_<name>_CREDENTIAL_PROVIDER`

Specifies the credential provider for the given registry. If not set, the providers in `registry.global-credential-providers` will be used.

If specified as a string, path and arguments will be split on spaces. For paths or arguments that contain spaces, use an array.

If the value exists in the `[credential-alias]` table, the alias will be used.

See Registry Authentication for more information.

#### `registries.crates-io.protocol`

- Type: string
- Default: `"sparse"`
- Environment: `CARGO_REGISTRIES_CRATES_IO_PROTOCOL`

Specifies the protocol used to access crates.io. Allowed values are `git` or `sparse`.

`git` causes Cargo to clone the entire index of all packages ever published to crates.io from https://github.com/rust-lang/crates.io-index/. This can have performance implications due to the size of the index. `sparse` is a newer protocol which uses HTTPS to download only what is necessary from https://index.crates.io/. This can result in a significant performance improvement for resolving new dependencies in most situations.

More information about registry protocols may be found in the Registries chapter.

### `[registry]`

The `[registry]` table controls the default registry used when one is not specified.

#### `registry.index`

This value is no longer accepted and should not be used.

#### `registry.default`

- Type: string
- Default: `"crates-io"`
- Environment: `CARGO_REGISTRY_DEFAULT`

The name of the registry (from the `registries` table) to use by default for registry commands like `cargo publish`.

Can be overridden with the `--registry` command-line option.

#### `registry.credential-provider`

- Type: string or array of path and arguments
- Default: none
- Environment: `CARGO_REGISTRY_CREDENTIAL_PROVIDER`

Specifies the credential provider for crates.io. If not set, the providers in `registry.global-credential-providers` will be used.

If specified as a string, path and arguments will be split on spaces. For paths or arguments that contain spaces, use an array.

If the value exists in the `[credential-alias]` table, the alias will be used.

See Registry Authentication for more information.

#### `registry.token`

- Type: string
- Default: none
- Environment: `CARGO_REGISTRY_TOKEN`

Specifies the authentication token for crates.io. This value should only appear in the credentials file. This is used for registry commands like `cargo publish` that require authentication.

Can be overridden with the `--token` command-line option.

#### `registry.global-credential-providers`

- Type: array
- Default: `["cargo:token"]`
- Environment: `CARGO_REGISTRY_GLOBAL_CREDENTIAL_PROVIDERS`

Specifies the list of global credential providers. If credential provider is not set for a specific registry using `registries.<name>.credential-provider`, Cargo will use the credential providers in this list. Providers toward the end of the list have precedence.

Path and arguments are split on spaces. If the path or arguments contains spaces, the credential provider should be defined in the `[credential-alias]` table and referenced here by its alias.

See Registry Authentication for more information.

### `[source]`

The `[source]` table defines the registry sources available. See Source Replacement for more information. It consists of a sub-table for each named source. A source should only define one kind (directory, registry, local-registry, or git).

#### `source.<name>.replace-with`

- Type: string
- Default: none
- Environment: not supported

If set, replace this source with the given named source or named registry.

#### `source.<name>.directory`

- Type: string (path)
- Default: none
- Environment: not supported

Sets the path to a directory to use as a directory source.

#### `source.<name>.registry`

- Type: string (url)
- Default: none
- Environment: not supported

Sets the URL to use for a registry source.

#### `source.<name>.local-registry`

- Type: string (path)
- Default: none
- Environment: not supported

Sets the path to a directory to use as a local registry source.

#### `source.<name>.git`

- Type: string (url)
- Default: none
- Environment: not supported

Sets the URL to use for a git repository source.

#### `source.<name>.branch`

- Type: string
- Default: none
- Environment: not supported

Sets the branch name to use for a git repository.

If none of `branch`, `tag`, or `rev` is set, defaults to the `master` branch.

#### `source.<name>.tag`

- Type: string
- Default: none
- Environment: not supported

Sets the tag name to use for a git repository.

If none of `branch`, `tag`, or `rev` is set, defaults to the `master` branch.

#### `source.<name>.rev`

- Type: string
- Default: none
- Environment: not supported

Sets the revision to use for a git repository.

If none of `branch`, `tag`, or `rev` is set, defaults to the `master` branch.

### `[target]`

The `[target]` table is used for specifying settings for specific platform targets. It consists of a sub-table which is either a platform triple or a `cfg()` expression. The given values will be used if the target platform matches either the `<triple>` value or the `<cfg>` expression.

    [target.thumbv7m-none-eabi]
    linker = "arm-none-eabi-gcc"
    runner = "my-emulator"
    rustflags = ["…", "…"]

    [target.'cfg(all(target_arch = "arm", target_os = "none"))']
    runner = "my-arm-wrapper"
    rustflags = ["…", "…"]

`cfg` values come from those built-in to the compiler (run `rustc --print=cfg` to view) and extra `--cfg` flags passed to `rustc` (such as those defined in `RUSTFLAGS`). Do not try to match on `debug_assertions`, `test`, Cargo features like `feature="foo"`, or values set by build scripts.

If using a target spec JSON file, the `<triple>` value is the filename stem. For example `--target foo/bar.json` would match `[target.bar]`.

#### `target.<triple>.ar`

This option is deprecated and unused.

#### `target.<triple>.linker`

- Type: string (program path)
- Default: none
- Environment: `CARGO_TARGET_<triple>_LINKER`

Specifies the linker which is passed to `rustc` (via `-C linker`) when the `<triple>` is being compiled for. By default, the linker is not overridden.

#### `target.<cfg>.linker`

This is similar to the target linker, but using a `cfg()` expression. If both a `<triple>` and `<cfg>` runner match, the `<triple>` will take precedence. It is an error if more than one `<cfg>` runner matches the current target.

#### `target.<triple>.runner`

- Type: string or array of strings (program path with args)
- Default: none
- Environment: `CARGO_TARGET_<triple>_RUNNER`

If a runner is provided, executables for the target `<triple>` will be executed by invoking the specified runner with the actual executable passed as an argument. This applies to `cargo run`, `cargo test` and `cargo bench` commands. By default, compiled executables are executed directly.

#### `target.<cfg>.runner`

This is similar to the target runner, but using a `cfg()` expression. If both a `<triple>` and `<cfg>` runner match, the `<triple>` will take precedence. It is an error if more than one `<cfg>` runner matches the current target.

#### `target.<triple>.rustflags`

- Type: string or array of strings
- Default: none
- Environment: `CARGO_TARGET_<triple>_RUSTFLAGS`

Passes a set of custom flags to the compiler for this `<triple>`. The value may be an array of strings or a space-separated string.

See `build.rustflags` for more details on the different ways to specific extra flags.

#### `target.<cfg>.rustflags`

This is similar to the target rustflags, but using a `cfg()` expression. If several `<cfg>` and `<triple>` entries match the current target, the flags are joined together.

#### `target.<triple>.rustdocflags`

- Type: string or array of strings
- Default: none
- Environment: `CARGO_TARGET_<triple>_RUSTDOCFLAGS`

Passes a set of custom flags to the compiler for this `<triple>`. The value may be an array of strings or a space-separated string.

See `build.rustdocflags` for more details on the different ways to specific extra flags.

#### `target.<triple>.<links>`

The links sub-table provides a way to override a build script. When specified, the build script for the given `links` library will not be run, and the given values will be used instead.

    [target.x86_64-unknown-linux-gnu.foo]
    rustc-link-lib = ["foo"]
    rustc-link-search = ["/path/to/foo"]
    rustc-flags = "-L /some/path"
    rustc-cfg = ['key="value"']
    rustc-env = {key = "value"}
    rustc-cdylib-link-arg = ["…"]
    metadata_key1 = "value"
    metadata_key2 = "value"

### `[term]`

The `[term]` table controls terminal output and interaction.

#### `term.quiet`

- Type: boolean
- Default: false
- Environment: `CARGO_TERM_QUIET`

Controls whether or not log messages are displayed by Cargo.

Specifying the `--quiet` flag will override and force quiet output. Specifying the `--verbose` flag will override and disable quiet output.

#### `term.verbose`

- Type: boolean
- Default: false
- Environment: `CARGO_TERM_VERBOSE`

Controls whether or not extra detailed messages are displayed by Cargo.

Specifying the `--quiet` flag will override and disable verbose output. Specifying the `--verbose` flag will override and force verbose output.

#### `term.color`

- Type: string
- Default: `"auto"`
- Environment: `CARGO_TERM_COLOR`

Controls whether or not colored output is used in the terminal. Possible values:

- `auto` (default): Automatically detect if color support is available on the terminal.
- `always`: Always display colors.
- `never`: Never display colors.

Can be overridden with the `--color` command-line option.

#### `term.hyperlinks`

- Type: bool
- Default: auto-detect
- Environment: `CARGO_TERM_HYPERLINKS`

Controls whether or not hyperlinks are used in the terminal.

#### `term.unicode`

- Type: bool
- Default: auto-detect
- Environment: `CARGO_TERM_UNICODE`

Control whether output can be rendered using non-ASCII unicode characters.

#### `term.progress.when`

- Type: string
- Default: `"auto"`
- Environment: `CARGO_TERM_PROGRESS_WHEN`

Controls whether or not progress bar is shown in the terminal. Possible values:

- `auto` (default): Intelligently guess whether to show progress bar.
- `always`: Always show progress bar.
- `never`: Never show progress bar.

#### `term.progress.width`

- Type: integer
- Default: none
- Environment: `CARGO_TERM_PROGRESS_WIDTH`

Sets the width for progress bar.

#### `term.progress.term-integration`

- Type: bool
- Default: auto-detect
- Environment: `CARGO_TERM_PROGRESS_TERM_INTEGRATION`

Report progress to the terminal emulator for display in places like the task bar.