What causes "command ["rustup", "check"] exited with code {}. stderr: {}" in jdx/mise?

Read the stderr in the message and run `rustup check` manually to reproduce the failure.

command ["rustup", "check"] exited with code {}. stderr: {}

Error message

command ["rustup", "check"] exited with code {}. stderr: {}

What it means

In outdated_info, mise runs `rustup check` unchecked because exit code 100 means 'updates available', not failure. Any other non-zero exit code (and any unknown/null exit code, treated as -1) is a real failure and is wrapped in this error along with rustup's trimmed stderr.

Source

Thrown at src/plugins/core/rust.rs:649

        let v_re = regex!(r#"Update available : (.*) -> (.*)"#);
        if regex!(r"(\d+)\.(\d+)\.(\d+)").is_match(&tv.version) {
            let oi = OutdatedInfo::resolve(config, tv.clone(), bump, opts).await?;
            Ok(oi)
        } else {
            let ts = config.get_toolset().await?;
            let runtime = RustRuntime::resolve_recorded_for_tool_version(config, tv).await?;
            let mut cmd = cmd(runtime.bin_dir.join(RUSTUP_BIN), ["check"])
                .env("PATH", self.path_env_for_cmd(config, tv).await?);
            for (k, v) in self.exec_env(config, ts, tv).await? {
                cmd = cmd.env(k, v);
            }
            // rustup check returns exit code 100 when updates are available
            // This is not an error, so we use unchecked() and check status manually
            let result = cmd.stdout_capture().stderr_capture().unchecked().run()?;
            let exit_code = result.status.code().unwrap_or(-1);
            if exit_code != 0 && exit_code != 100 {
                let stderr = String::from_utf8_lossy(&result.stderr);
                eyre::bail!(
                    "command [\"rustup\", \"check\"] exited with code {}. stderr: {}",
                    exit_code,
                    stderr.trim()
                );
            }
            let out = String::from_utf8_lossy(&result.stdout);
            for line in out.lines() {
                if line.starts_with(&self.target_triple(tv))
                    && let Some(_cap) = v_re.captures(line)
                {
                    // let requested = cap.get(1).unwrap().as_str().to_string();
                    // let latest = cap.get(2).unwrap().as_str().to_string();
                    let oi = OutdatedInfo::new(config, tv.clone(), tv.version.clone())?;
                    return Ok(Some(oi));
                }
            }
            Ok(None)
        }

View on GitHub (pinned to afd2eddd3a)

Solutions

Read the stderr in the message and run `rustup check` manually to reproduce the failure.
Fix network/proxy access to rust's release servers (set HTTPS_PROXY or allowlist static.rust-lang.org).
Repair or reinstall rustup (`rustup self update`, or fresh install).
Ensure the `rustup` on PATH is the real rustup, not a shim returning unexpected exit codes.

Example fix

// before: offline CI
$ mise outdated
command ["rustup", "check"] exited with code 1. stderr: error: could not download...
// after: configure proxy in CI
export HTTPS_PROXY=http://proxy.internal:8080
$ mise outdated

Defensive patterns

Strategy: try-catch

Validate before calling

match std::process::Command::new("rustup").arg("check").output() {
    Ok(o) if o.status.code().map_or(true, |c| c != 0 && c != 100) => {
        eprintln!("rustup check unhealthy: {}", String::from_utf8_lossy(&o.stderr));
    }
    _ => {}
}

Try / catch

match outcome {
    Err(e) if e.to_string().contains("command [\"rustup\", \"check\"]") => {
        eprintln!("fix rustup/network before checking outdated rust: {}", e);
        // check connectivity to static.rust-lang.org, reinstall rustup
    }
    ...
}

Prevention

Ensure CI has network/proxy access to static.rust-lang.org.
Run `rustup check` in your environment before `mise outdated` to catch breakage early.
Keep rustup healthy with periodic `rustup self update`.
Don't shadow the real rustup binary with shims returning odd exit codes.

When it happens

Trigger: Running `mise outdated` / version-check paths for rust when `rustup check` exits with a code other than 0 or 100: rustup binary missing/broken, network failure reaching the release server, corrupted RUSTUP_HOME, or rustup killed by a signal (null exit code → -1).

Common situations: Offline CI runners where rustup check cannot reach static.rust-lang.org; broken rustup installs; proxy/firewall blocking rustup's telemetry; a non-rustup `rustup` shim on PATH that exits with an unexpected code.

Related errors

AI-assisted analysis of jdx/mise@afd2eddd3a (2026-09-09). Data as JSON: /api/errors/1176721d5d7692ed. Report an issue: GitHub.