txthinking/brook · error

You forgot the --prometheusPath

Error message

You forgot the --prometheusPath

What it means

When --prometheus is enabled, brook exposes metrics on an HTTP path that must be given via --prometheusPath. If --prometheus is set but --prometheusPath is empty, the CLI refuses to start. It prevents silently mounting metrics at an empty/unusable path.

Source

Thrown at cli/brook/main.go:242

			if err != nil {
				return err
			}
			p.TouchBrook()
		}
		if c.String("dialWithNIC") != "" {
			p := dialwithnic.NewDialWithNIC(c.String("dialWithNIC"))
			p.TouchBrook()
		}
		if c.String("dialWithSocks5") != "" {
			p, err := socks5dial.NewSocks5Dial(c.String("dialWithSocks5"), c.String("dialWithSocks5Username"), c.String("dialWithSocks5Password"), c.Int("dialWithSocks5TCPTimeout"), c.Int("dialWithSocks5UDPTimeout"))
			if err != nil {
				return err
			}
			p.TouchBrook()
		}
		if c.String("prometheus") != "" {
			if c.String("prometheusPath") == "" {
				return errors.New("You forgot the --prometheusPath")
			}
			var m map[string]string
			if len(c.StringSlice("tag")) > 0 {
				m = make(map[string]string)
				for _, v := range c.StringSlice("tag") {
					l := strings.Split(v, ":")
					if len(l) != 2 {
						return errors.New("Invalid tag " + v)
					}
					m[l[0]] = l[1]
				}
			}
			p := prometheus.NewPrometheus(c.String("prometheus"), c.String("prometheusPath"), m)
			p.TouchBrook()
			g.Add(&runnergroup.Runner{
				Start: func() error {
					return p.ListenAndServe()
				},

View on GitHub (pinned to 5cd13ef3b1)

Solutions

1. Add --prometheusPath /metrics (or your desired path) alongside --prometheus
2. Remove --prometheus if metrics are not needed
3. Set both flags together in your service template

Example fix

// before
brook server -l :9999 --prometheus 127.0.0.1:18080
// after
brook server -l :9999 --prometheus 127.0.0.1:18080 --prometheusPath /metrics

if prometheusAddr != "" && prometheusPath == "" {
	return errors.New("--prometheus requires --prometheusPath")
}

When it happens

Trigger: Running any subcommand with --prometheus but without --prometheusPath, e.g. --prometheus 127.0.0.1:18080.

Common situations: Copying prometheus flags from docs that mention only --prometheus; configs where the path flag was dropped during refactoring of service definitions.

Understand the failure class

Background: "--flag is required" and "must specify" CLI errors: how missing-required-flag validation works and how to fix it — this error's family across 20 libraries.

Related errors

• --pid must be with absolute path
• --log must be with absolute path
• Invalid tag
• --blockDomainList must be with absolute path
• --blockCIDR4List must be with absolute path

AI-assisted analysis of txthinking/brook@5cd13ef3b1 (2026-09-06). Data as JSON: /api/errors/5179bfe25c280b54. Report an issue: GitHub.