lima-vm/lima · error

failed to marshal instance config: %w

Error message

failed to marshal instance config: %w

What it means

handleInspectStatusAction serializes the Instance with inst.MarshalJSON() to pipe it to the external driver's --inspect-status subcommand. This error means that custom JSON marshaling failed, which is rare and usually indicates an inconsistent in-memory Instance (e.g. a field that cannot be encoded, such as an invalid value in a custom marshaler).

Source

Thrown at pkg/driverutil/vm.go:90

	var stderrBuf bytes.Buffer
	cmd.Stderr = &stderrBuf

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return "", err
	}
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return "", err
	}
	if err := cmd.Start(); err != nil {
		return "", err
	}

	encoder := json.NewEncoder(stdin)
	payload, err := inst.MarshalJSON()
	if err != nil {
		return "", fmt.Errorf("failed to marshal instance config: %w", err)
	}
	if err := encoder.Encode(payload); err != nil {
		return "", err
	}
	stdin.Close()

	decoder := json.NewDecoder(stdout)
	var response []byte
	if err := decoder.Decode(&response); err != nil {
		return "", err
	}

	var respInst limatype.Instance
	if err := respInst.UnmarshalJSON(response); err != nil {
		return "", fmt.Errorf("failed to unmarshal instance response: %w", err)
	}

	if err := cmd.Wait(); err != nil {

View on GitHub (pinned to dd909d0973)

Solutions

1. Look at the wrapped error to identify which field failed to marshal
2. Validate and fix the corresponding field in ~/.lima/<instance>/lima.yaml (URLs, enums, sizes)
3. Reload the instance through the standard load path so fields are normalized/defaulted
4. Report or upgrade if a Lima version regression in MarshalJSON is suspected; pin a working version

Example fix

// before: lima.yaml
additionalDisks: ["disk:"] // malformed
// after
additionalDisks:
  - name: "data"

if _, err := inst.MarshalJSON(); err != nil {
    return fmt.Errorf("instance not marshalable, fix lima.yaml: %w", err)
}

status, err := driverutil.InspectStatus(ctx, inst)
if err != nil {
    if strings.Contains(err.Error(), "failed to marshal instance config") {
        var jerr *json.UnsupportedTypeError
        if errors.As(err, &jerr) {
            log.Errorf("bad field: %v", jerr.Value)
        }
    }
    return err
}

When it happens

Trigger: Calling InspectStatus on an external-driver instance where limatype.Instance.MarshalJSON returns an error — typically due to a field with a custom MarshalJSON that errors on the current instance state (invalid enum/URL/time value loaded from lima.yaml).

Common situations: Manually edited lima.yaml with a value the custom marshaler rejects (bad URL, out-of-range enum); programmatically constructed Instance missing required fields; a Lima version mismatch where the marshaler changed behavior.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• failed to unmarshal instance response: %w
• failed to marshal as JSON: %+v: %w
• failed to marshal instance %#q: %w
• failed to write driver PID file: %w
• failed to create driver client: %w

AI-assisted analysis of lima-vm/lima@dd909d0973 (2026-09-01). Data as JSON: /api/errors/bdd5a81b751693e0. Report an issue: GitHub.