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                        <h1 id="overrides"><a class="header" href="#overrides">Overrides</a></h1>
<p><code>rustup</code> automatically determines which <a href="concepts/toolchains.html">toolchain</a> to use when one of the
installed commands like <code>rustc</code> is executed. There are several ways to control
and override which toolchain is used:</p>
<ol>
<li>A <a href="#toolchain-override-shorthand">toolchain override shorthand</a> used on the command-line, such as <code>cargo +beta</code>.</li>
<li>The <code>RUSTUP_TOOLCHAIN</code> environment variable.</li>
<li>A <a href="#directory-overrides">directory override</a>, set with the <code>rustup override</code> command.</li>
<li>The <a href="#the-toolchain-file"><code>rust-toolchain.toml</code></a> file.</li>
<li>The <a href="#default-toolchain">default toolchain</a>.</li>
</ol>
<p>The toolchain is chosen in the order listed above, using the first one that is
specified. There is one exception though: directory overrides and the
<code>rust-toolchain.toml</code> file are also preferred by their proximity to the current
directory. That is, these two override methods are discovered by walking up
the directory tree toward the filesystem root, and a <code>rust-toolchain.toml</code> file
that is closer to the current directory will be preferred over a directory
override that is further away.</p>
<p>To verify which toolchain is active, you can use <code>rustup show</code>.</p>
<h2 id="toolchain-override-shorthand"><a class="header" href="#toolchain-override-shorthand">Toolchain override shorthand</a></h2>
<p>The <code>rustup</code> toolchain proxies can be instructed directly to use a specific
toolchain, a convenience for developers who often test different toolchains.
If the first argument to <code>cargo</code>, <code>rustc</code> or other tools in the toolchain
begins with <code>+</code>, it will be interpreted as a <code>rustup</code> toolchain name, and that
toolchain will be preferred, as in</p>
<pre><code class="language-console">cargo +beta test
</code></pre>
<h2 id="directory-overrides"><a class="header" href="#directory-overrides">Directory overrides</a></h2>
<p>Directories can be assigned their own Rust toolchain with <code>rustup override</code>.
When a directory has an override then any time <code>rustc</code> or <code>cargo</code> is run
inside that directory, or one of its child directories, the override toolchain
will be invoked.</p>
<p>To use to a specific nightly for a directory:</p>
<pre><code class="language-console">rustup override set nightly-2014-12-18
</code></pre>
<p>Or a specific stable release:</p>
<pre><code class="language-console">rustup override set 1.0.0
</code></pre>
<p>To see the active toolchain use <code>rustup show</code>. To remove the override and use
the default toolchain again, <code>rustup override unset</code>.</p>
<p>The per-directory overrides are stored in <a href="configuration.html">a configuration file</a> in <code>rustup</code>’s
home directory.</p>
<h2 id="the-toolchain-file"><a class="header" href="#the-toolchain-file">The toolchain file</a></h2>
<p>Some projects find themselves ‘pinned’ to a specific release of Rust and want
this information reflected in their source repository. This is most often the
case for nightly-only software that pins to a revision from the release
archives.</p>
<p>In these cases the toolchain can be named in the project’s directory in a file
called <code>rust-toolchain.toml</code> or <code>rust-toolchain</code>. If both files are present in
a directory, the latter is used for backwards compatibility. The files use the
<a href="https://toml.io/">TOML</a> format and have the following layout:</p>
<pre><code class="language-toml">[toolchain]
channel = "nightly-2020-07-10"
components = [ "rustfmt", "rustc-dev" ]
targets = [ "wasm32-unknown-unknown", "thumbv2-none-eabi" ]
profile = "minimal"
</code></pre>
<p>The <code>[toolchain]</code> section is mandatory, and at least one property must be
specified. <code>channel</code> and <code>path</code> are mutually exclusive.</p>
<p>For backwards compatibility, <code>rust-toolchain</code> files also support a legacy
format that only contains a toolchain name without any TOML encoding, e.g.
just <code>nightly-2021-01-21</code>. The file has to be encoded in US-ASCII in this case
(if you are on Windows, check the encoding and that it does not start with a
BOM). The legacy format is not available in <code>rust-toolchain.toml</code> files.</p>
<p>If you see the following error (when running <code>rustc</code>, <code>cargo</code> or other command)</p>
<pre><code>error: invalid channel name '[toolchain]' in '/PATH/TO/DIRECTORY/rust-toolchain'
</code></pre>
<p>it means you’re running <code>rustup</code> pre-1.23.0 and trying to interact with a project
that uses the new TOML encoding in the <code>rust-toolchain</code> file. You need to upgrade
<code>rustup</code> to 1.23.0+.</p>
<p>The <code>rust-toolchain.toml</code>/<code>rust-toolchain</code> files are suitable to check in to
source control. If that’s done, <code>Cargo.lock</code> should probably be tracked too if
the toolchain is pinned to a specific release, to avoid potential compatibility
issues with dependencies.</p>
<h3 id="toolchain-file-settings"><a class="header" href="#toolchain-file-settings">Toolchain file settings</a></h3>
<h4 id="channel"><a class="header" href="#channel">channel</a></h4>
<p>The <code>channel</code> setting specifies which <a href="concepts/toolchains.html">toolchain</a> to use. The value is a
string in the following form:</p>
<pre><code>(&lt;channel&gt;[-&lt;date&gt;])|&lt;custom toolchain name&gt;

&lt;channel&gt;       = stable|beta|nightly|&lt;versioned&gt;[-&lt;prerelease&gt;]
&lt;versioned&gt;     = &lt;major.minor&gt;|&lt;major.minor.patch&gt;
&lt;prerelease&gt;    = beta[.&lt;number&gt;]
&lt;date&gt;          = YYYY-MM-DD
</code></pre>
<h4 id="path"><a class="header" href="#path">path</a></h4>
<p>The <code>path</code> setting allows a custom toolchain to be used. The value is an
absolute path string.</p>
<p>Since a <code>path</code> directive directly names a local toolchain, other options
like <code>components</code>, <code>targets</code>, and <code>profile</code> have no effect.</p>
<p><code>channel</code> and <code>path</code> are mutually exclusive, since a <code>path</code> already
points to a specific toolchain.</p>
<h4 id="profile"><a class="header" href="#profile">profile</a></h4>
<p>The <code>profile</code> setting names a group of components to be installed. The
value is a string. The valid options are: <code>minimal</code>, <code>default</code>, and
<code>complete</code>. See <a href="concepts/profiles.html">profiles</a> for details of each.</p>
<p>Note that if not specified, the <code>default</code> profile is not necessarily
used, as a different default profile might have been set with <code>rustup set profile</code>.</p>
<h4 id="components"><a class="header" href="#components">components</a></h4>
<p>The <code>components</code> setting contains a list of additional components to
install. The value is a list of strings. See <a href="concepts/components.html">components</a> for a list of
components. Note that different toolchains may have different components
available.</p>
<p>The components listed here are additive with the current profile.</p>
<h4 id="targets"><a class="header" href="#targets">targets</a></h4>
<p>The <code>targets</code> setting contains a list of platforms to install for
<a href="https://rust-lang.github.io/rustup/cross-compilation.html">cross-compilation</a>. The value is a list of strings.</p>
<p>The host platform is automatically included; the targets listed here are
additive.</p>
<h2 id="default-toolchain"><a class="header" href="#default-toolchain">Default toolchain</a></h2>
<p>If no other overrides are set, the global default toolchain will be used. This
default can be chosen when <code>rustup</code> is <a href="installation/index.html">installed</a>. The <code>rustup default</code>
command can be used to set and query the current default. Run <code>rustup default</code>
without any arguments to print the current default. Specify a toolchain as an
argument to change the default:</p>
<pre><code class="language-console">rustup default nightly-2020-07-27
</code></pre>

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