nats-io/nats-server · warning

%s: config has no values or is empty

Error message

%s: config has no values or is empty

What it means

A non-fatal warning emitted during Options.processConfigFile when the parsed configuration map is empty (len(m) == 0). The config file existed but contained no values, so the server proceeds with defaults while reporting this warning through processConfigErr.Warnings(). It is intentionally a warning, not an error, so startup is not blocked.

Source

Thrown at server/opts.go:1100

	m, err := conf.ParseWithChecks(data)
	if err != nil {
		return err
	}

	return o.processConfigFile(_EMPTY_, m)
}

// ConfigDigest returns the digest representing the configuration.
func (o *Options) ConfigDigest() string {
	return o.configDigest
}

func (o *Options) processConfigFile(configFile string, m map[string]any) error {
	// Collect all errors and warnings and report them all together.
	errors := make([]error, 0)
	warnings := make([]error, 0)
	if len(m) == 0 {
		warnings = append(warnings, fmt.Errorf("%s: config has no values or is empty", configFile))
	}

	// First check whether a system account has been defined,
	// as that is a condition for other features to be enabled.
	if err := configureSystemAccount(o, m); err != nil {
		errors = append(errors, err)
	}

	for k, v := range m {
		o.processConfigFileLine(k, v, &errors, &warnings)
	}

	// Post-process: check auth callout allowed accounts against configured accounts.
	if o.AuthCallout != nil {
		accounts := make(map[string]struct{})
		for _, acc := range o.Accounts {
			accounts[acc.Name] = struct{}{}
		}

View on GitHub (pinned to 3a66a489d2)

Solutions

1. Add at least one setting (e.g. port or listen) to the config file.
2. Verify the -c flag points to the intended file and that the file is non-empty on disk.
3. If defaults are intended, ignore the warning — the server continues with default options.
4. Check your config generation/templating pipeline for a rendering failure producing empty output.

Example fix

// before (empty server.conf)
# nothing here
// after (server.conf)
port: 4222
listen: 0.0.0.0:4222

// before passing -c to the server
data, err := os.ReadFile(configFile)
if err != nil || len(bytes.TrimSpace(data)) == 0 {
	return fmt.Errorf("config file %s is empty or unreadable", configFile)
}

When it happens

Trigger: Passing a config file path (-c) whose file is empty, contains only comments/whitespace, or parses to an empty map.

Common situations: A freshly created placeholder config; a file with only comments; the wrong file passed; a templating tool that rendered an empty file.

Related errors

• mqtt authentication token not compatible with presence of us
• ack wait must be a positive value
• JS API timeout must be a positive value
• mqtt requires JetStream to be enabled if running in standalo
• unable to plug TLS verify connection, config is nil

AI-assisted analysis of nats-io/nats-server@3a66a489d2 (2026-09-02). Data as JSON: /api/errors/d730bc72fec3e5f3. Report an issue: GitHub.