rust-lang/mdBook · error

no address found for {}

Error message

no address found for {}

What it means

`mdbook serve` resolves the --hostname/--port (or the address string) into a SocketAddr via ToSocketAddrs and takes the first result. If resolution yields no addresses, serving cannot proceed and this error is raised with the original address string.

Source

Thrown at src/cmd/serve.rs:75

    let open_browser = args.get_flag("open");

    let address = format!("{hostname}:{port}");

    let update_config = |book: &mut MDBook| {
        book.config
            .set("output.html.live-reload-endpoint", LIVE_RELOAD_ENDPOINT)
            .expect("live-reload-endpoint update failed");
        set_dest_dir(args, book);
        // Override site-url for local serving of the 404 file
        book.config.set("output.html.site-url", "/").unwrap();
    };
    update_config(&mut book);
    book.build()?;

    let sockaddr: SocketAddr = address
        .to_socket_addrs()?
        .next()
        .ok_or_else(|| anyhow::anyhow!("no address found for {}", address))?;
    let build_dir = book.build_dir_for("html");
    let html_config = book.config.html_config().unwrap_or_default();
    let file_404 = html_config.get_404_output_file();

    // A channel used to broadcast to any websockets to reload when a file changes.
    let (tx, _rx) = tokio::sync::broadcast::channel::<Message>(100);

    let reload_tx = tx.clone();
    let thread_handle = std::thread::spawn(move || {
        serve(build_dir, sockaddr, reload_tx, &file_404);
    });

    let serving_url = format!("http://{address}");
    info!("Serving on: {}", serving_url);

    if open_browser {
        open(serving_url);
    }

View on GitHub (pinned to dc21064fc2)

Solutions

1. Use an explicit address like `mdbook serve -n 127.0.0.1 -p 3000` (or `localhost`) instead of an unresolvable hostname.
2. Check DNS/network connectivity: verify the hostname resolves (`getent hosts <host>` or `nslookup <host>`).
3. Correct the --hostname value or the address passed in the serve command/config.

Example fix

// before
mdbook serve --hostname mybox.internal --port 3000

// after
mdbook serve --hostname 127.0.0.1 --port 3000

// Pre-check address resolution
require('dns').lookup(host, (err) => { if (err) console.error(`cannot resolve ${host}`); });

// Rust
match mdbook::cmd::serve::execute(args) {
    Err(e) if e.to_string().starts_with("no address found") => {
        eprintln!("Unresolvable hostname; try --hostname 127.0.0.1: {e}");
        std::process::exit(1);
    }
    res => res,
}

When it happens

Trigger: Running mdbook serve with a hostname that DNS cannot resolve (or no results from to_socket_addrs), e.g. `mdbook serve -n bad.host.example` or an unresolvable interface name; the iterator .next() is None.

Common situations: Typo in the --hostname flag; using a hostname only resolvable on another network (VPN/corporate DNS); offline machine with a hostname instead of 127.0.0.1/localhost; container without DNS configured.

Related errors

• Unable to bind to {address}: {e}
• redirect entry for `{original}` only has source paths with `
• theme dir {} does not exist
• redirect found for existing chapter at `{path}` Either delet
• [output.html.search.chapter] key `{}` does not match any cha

AI-assisted analysis of rust-lang/mdBook@dc21064fc2 (2026-09-01). Data as JSON: /api/errors/4a9c1eabb679e93c. Report an issue: GitHub.