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 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

[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 .cargo directory containing `config.toml`, make absolute
ENV_VAR_NAME_3 = { value = "relative/path", relative = true }

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

[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
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.
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.
strip = "none"           # Removes symbols or debuginfo.
[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`).

[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]
quiet = false          # whether cargo output is quiet
verbose = false        # whether cargo provides verbose output
color = 'auto'         # whether cargo colorizes output
progress.when = 'auto' # whether cargo shows progress bar
progress.width = 80    # width of progress bar

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:

cargo --config net.git-fetch-with-cli=true 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.

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 …

The --config option can also be used to pass paths to extra configuration files that Cargo should use for a specific invocation. Options from configuration files loaded this way follow the same precedence rules as other options specified directly with --config.

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.

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.

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. 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.

`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.

This allows passing either a string or an array of strings. Each string value is a target platform triple. The selected build targets will be built for each of the selected architectures.

The string value may also be a relative path to a .json target spec file.

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.

`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:

CARGO_ENCODED_RUSTFLAGS environment variable.
RUSTFLAGS environment variable.
All matching target.<triple>.rustflags and target.<cfg>.rustflags config entries joined together.
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 three mutually exclusive sources of extra flags. They are checked in order, with the first one being used:

CARGO_ENCODED_RUSTDOCFLAGS environment variable.
RUSTDOCFLAGS environment variable.
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. 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

`[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.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
default: See profile docs.
Environment: CARGO_PROFILE_<name>_STRIP

See strip.

`[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), 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.<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>.<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"