grafana/k6 · error

logfile configuration should be in the form `file=path-to-lo

Error message

logfile configuration should be in the form `file=path-to-local-file` but is `%s`

What it means

A validation guard in FileHookFromConfigLine. The --log-output flag for file logging must be exactly `file=path`; it fires when the prefix before '=' is not 'file' (e.g. a malformed line or a different output type routed here). The at-fault input is the whole log-output configuration line.

Source

Thrown at internal/log/file.go:50

	bw             *bufio.Writer
	levels         []logrus.Level
}

// FileHookFromConfigLine returns new fileHook hook.
func FileHookFromConfigLine(
	fs fsext.Fs, getCwd func() (string, error),
	fallbackLogger logrus.FieldLogger, line string,
) (AsyncHook, error) {
	hook := &fileHook{
		fs:             fs,
		fallbackLogger: fallbackLogger,
		levels:         logrus.AllLevels,
		loglines:       make(chan []byte, fileHookBufferSize),
	}

	logOutput, _, _ := strings.Cut(line, "=")
	if logOutput != "file" {
		return nil, fmt.Errorf("logfile configuration should be in the form `file=path-to-local-file` but is `%s`", line)
	}
	if err := hook.parseArgs(line); err != nil {
		return nil, err
	}
	if err := hook.openFile(getCwd); err != nil {
		return nil, err
	}
	return hook, nil
}

func (h *fileHook) parseArgs(line string) error {
	tokens, err := strvals.Parse(line)
	if err != nil {
		return fmt.Errorf("error while parsing logfile configuration %w", err)
	}

	for _, token := range tokens {
		switch token.Key {

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Use the format file=path-to-local-file for --log-output
2. Do not pass other output kinds to the file hook; use the appropriate --log-output value (e.g. stdout, loki)
3. Check for typos or extra whitespace before '='

When it happens

Trigger: Thrown at internal/log/file.go:50 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/fddc328a0892d724. Report an issue: GitHub.