caddyserver/caddy · error

cannot adapt config without config file (use --config)

Error message

cannot adapt config without config file (use --config)

What it means

loadConfigWithLogger rejects the combination --adapter <name> with no --config: an adapter only transforms file content, so naming one without input is ambiguous. It points you at --config explicitly because stdin alone ('-') also requires being named via --config -.

Source

Thrown at cmd/main.go:155

	// adapter is not empty,
	// adapter is not "caddyfile",
	// extension is not ".json",
	// extension is not ".caddyfile"
	// file does not start with "Caddyfile"
	return false, nil
}

func loadConfigWithLogger(logger *zap.Logger, configFile, adapterName string) ([]byte, string, string, error) {
	// if no logger is provided, use a nop logger
	// just so we don't have to check for nil
	if logger == nil {
		logger = zap.NewNop()
	}

	// specifying an adapter without a config file is ambiguous
	if adapterName != "" && configFile == "" {
		return nil, "", "", fmt.Errorf("cannot adapt config without config file (use --config)")
	}

	// load initial config and adapter
	var config []byte
	var cfgAdapter caddyconfig.Adapter
	var err error
	if configFile != "" {
		if configFile == "-" {
			config, err = io.ReadAll(os.Stdin)
			if err != nil {
				return nil, "", "", fmt.Errorf("reading config from stdin: %v", err)
			}
			logger.Info("using config from stdin")
		} else {
			config, err = os.ReadFile(configFile)
			if err != nil {
				return nil, "", "", fmt.Errorf("reading config from file: %v", err)
			}

View on GitHub (pinned to 50e54ee279)

Solutions

1. Add --config with a path, or --config - to read stdin

Example fix

# before
caddy adapt --adapter caddyfile

# after
caddy adapt --config Caddyfile --adapter caddyfile
cat Caddyfile | caddy adapt --config - --adapter caddyfile

if adapterName != "" && configFile == "" { return errors.New("--adapter requires --config (use '--config -' for stdin)") }

When it happens

Trigger: Running 'caddy adapt --adapter caddyfile' with no --config; piping a config to stdin but forgetting --config -; 'caddy run --adapter json' with no file.

Common situations: Users assuming the adapter flag implies reading stdin; copy-pasted commands that dropped the --config part.

Related errors

• adapting config using %s: %v
• invalid admin address %s: %v
• caddy responded with error: HTTP %d: %s
• no config file to load; either use --config flag or ensure C
• unmarshaling admin listener address from config: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/a6f273180a888c38. Report an issue: GitHub.