| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Create a new child process duplicating the parent process (see fork(2))."><meta name="keywords" content="rust, rustlang, rust-lang, fork"><title>fork in nix::unistd - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../nix/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../nix/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In nix::unistd</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Function <a href="../index.html">nix</a>::<wbr><a href="index.html">unistd</a>::<wbr><a class="fn" href="#">fork</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../src/nix/unistd.rs.html#292-300">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust fn"><code>pub unsafe fn fork() -> <a class="type" href="../type.Result.html" title="type nix::Result">Result</a><<a class="enum" href="enum.ForkResult.html" title="enum nix::unistd::ForkResult">ForkResult</a>></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Create a new child process duplicating the parent process (<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html">see |
| fork(2)</a>).</p> |
| <p>After successfully calling the fork system call, a second process will |
| be created which is identical to the original except for the pid and the |
| return value of this function. As an example:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>nix::{sys::wait::waitpid,unistd::{fork, ForkResult, write}}; |
| |
| <span class="kw">match unsafe</span>{fork()} { |
| <span class="prelude-val">Ok</span>(ForkResult::Parent { child, .. }) => { |
| <span class="macro">println!</span>(<span class="string">"Continuing execution in parent process, new child has pid: {}"</span>, child); |
| waitpid(child, <span class="prelude-val">None</span>).unwrap(); |
| } |
| <span class="prelude-val">Ok</span>(ForkResult::Child) => { |
| <span class="comment">// Unsafe to use `println!` (or `unwrap`) here. See Safety. |
| </span>write(libc::STDOUT_FILENO, <span class="string">"I'm a new child process\n"</span>.as_bytes()).ok(); |
| <span class="kw">unsafe </span>{ libc::_exit(<span class="number">0</span>) }; |
| } |
| <span class="prelude-val">Err</span>(<span class="kw">_</span>) => <span class="macro">println!</span>(<span class="string">"Fork failed"</span>), |
| }</code></pre></div> |
| <p>This will print something like the following (order nondeterministic). The |
| thing to note is that you end up with two processes continuing execution |
| immediately after the fork call but with different match arms.</p> |
| <div class="example-wrap"><pre class="language-text"><code>Continuing execution in parent process, new child has pid: 1234 |
| I'm a new child process</code></pre></div><h2 id="safety"><a href="#safety">Safety</a></h2> |
| <p>In a multithreaded program, only <a href="https://man7.org/linux/man-pages/man7/signal-safety.7.html">async-signal-safe</a> functions like <code>pause</code> |
| and <code>_exit</code> may be called by the child (the parent isn’t restricted). Note |
| that memory allocation may <strong>not</strong> be async-signal-safe and thus must be |
| prevented.</p> |
| <p>Those functions are only a small subset of your operating system’s API, so |
| special care must be taken to only invoke code you can control and audit.</p> |
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