grafana/k6 · error

unknown loki config key %s

Error message

unknown loki config key %s

What it means

parseArgs encountered a key=value pair in the Loki config line whose key matches no known option (loki, pushPeriod, profile, limit, msgMaxSize, level, allowedLabels) and no label./header. prefix. The offending key is the unknown configuration key.

Source

Thrown at internal/log/loki.go:195

			if opts.MsgMaxSize < 1 {
				return fmt.Errorf("loki msgMaxSize needs to be a positive number, is %d", opts.MsgMaxSize)
			}
		case "level":
			opts.Level = value
		case "allowedLabels":
			opts.AllowedLabels = strings.Split(value, ",")
		default:
			if after, ok := strings.CutPrefix(key, "label."); ok {
				opts.Labels = append(opts.Labels, [2]string{after, value})

				continue
			} else if after, ok := strings.CutPrefix(key, "header."); ok {
				opts.Headers = append(opts.Headers, [2]string{after, value})

				continue
			}

			return fmt.Errorf("unknown loki config key %s", key)
		}
	}

	return nil
}

// Listen fills one of two equally sized slices
// with entries and then push it while filling the other one.
//
// TODO benchmark this
//
//nolint:funlen,gocognit
func (h *lokiHook) Listen(ctx context.Context) {
	var (
		msgs       = make([]tmpMsg, h.limit)
		msgsToPush = make([]tmpMsg, h.limit)
		dropped    int
		count      int

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Correct the misspelled key or remove it from the Loki config line
2. Use label.<name>=<value> or header.<name>=<value> for custom labels and headers

When it happens

Trigger: Thrown at internal/log/loki.go:195 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/605da63b58bbc26d. Report an issue: GitHub.