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
  • /projects/foo/bar/.cargo/config
  • /projects/foo/.cargo/config
  • /projects/.cargo/config
  • /.cargo/config
  • $CARGO_HOME/config which defaults to:
    • Windows: %USERPROFILE%\.cargo\config
    • Unix: $HOME/.cargo/config

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.

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"
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`
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 all generated 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
pipelining = true         # rustc pipelining

[cargo-new]
name = "Your Name"        # name to use in `authors` field
email = "you@example.com" # email address to use in `authors` field
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
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 = 2                   # network retries
git-fetch-with-cli = true   # use the `git` executable for git operations
offline = false             # do not access the network

[registries.<name>]  # registries other than crates.io
index = "…"          # URL of the registry index
token = "…"          # authentication token for the registry

[registry]
default = "…"        # name of the default registry
token = "…"          # authentication token for crates.io

[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`

[target.<cfg>]
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]
verbose = false        # whether cargo provides verbose output
color = 'auto'         # whether cargo colorizes output

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.

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

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. For config files, that is relative to the parent directory of the .cargo directory where the value was defined. For environment variables it is relative to the current working directory.

# 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` is located.
# For example, `/my/project/.cargo/config` would result in `/my/project/vendor`.
directory = "vendor"

Credentials

Configuration values with sensitive information are stored in the $CARGO_HOME/credentials file. This file is automatically created and updated by cargo login. 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

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.

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.

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 Specifying 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"
t = "test"
r = "run"

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

[build]

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

build.jobs
  • Type: integer
  • Default: number of logical CPUs
  • Environment: CARGO_BUILD_JOBS

Sets the maximum number of compiler processes to run in parallel.

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 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
  • Default: host platform
  • Environment: CARGO_BUILD_TARGET

The default target platform triple to compile to.

This may also be a relative path to a .json target spec file.

Can be overridden with the --target CLI option.

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.

build.rustflags
  • Type: string or array of strings
  • Default: none
  • Environment: CARGO_BUILD_RUSTFLAGS or RUSTFLAGS

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

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

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

build.rustdocflags
  • Type: string or array of strings
  • Default: none
  • Environment: CARGO_BUILD_RUSTDOCFLAGS or RUSTDOCFLAGS

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

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

  1. RUSTDOCFLAGS environment variable.
  2. build.rustdocflags config value.

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

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.

Cargo saves a "dep info" file with a .d suffix which is a Makefile-like syntax that indicates all of the file dependencies required to rebuild the artifact. These are intended to be used with external build systems so that they can detect if Cargo needs to be re-executed. The paths in the file are absolute by default. This config setting can be set to strip the given prefix from all of the 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
  • Type: boolean
  • Default: true
  • Environment: CARGO_BUILD_PIPELINING

Controls whether or not build pipelining is used. This allows Cargo to schedule overlapping invocations of rustc in parallel when possible.

[cargo-new]

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

cargo-new.name
  • Type: string
  • Default: from environment
  • Environment: CARGO_NAME or CARGO_CARGO_NEW_NAME

Defines the name to use in the authors field when creating a new Cargo.toml file. If not specified in the config, Cargo searches the environment or your git configuration as described in the cargo new documentation.

cargo-new.email
  • Type: string
  • Default: from environment
  • Environment: CARGO_EMAIL or CARGO_CARGO_NEW_EMAIL

Defines the email address used in the authors field when creating a new Cargo.toml file. If not specified in the config, Cargo searches the environment or your git configuration as described in the cargo new documentation. The email value may be set to an empty string to prevent Cargo from placing an address in the authors field.

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.

[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=cargo::ops::registry=debug environment variable (or use 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.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.

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: 2
  • 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.

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.

[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 git 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.

[registry]

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

registry.index

This value is deprecated 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.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.

[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.

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), values set by build scripts, and extra --cfg flags passed to rustc (such as those defined in RUSTFLAGS). Do not try to match on debug_assertions or Cargo features like feature="foo".

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.<triple>.runner
  • Type: string or array of strings (program path and 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.

The value may be an array of strings like ['/path/to/program', 'somearg'] or a space-separated string like '/path/to/program somearg'. The arguments will be passed to the runner with the executable to run as the last argument. If the runner program does not have path separators, it will search PATH for the runner executable.

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 a 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>.<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.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.