k3s-io/k3s · error

invalid output format: {cfg.Output}

Error message

invalid output format: {cfg.Output}

What it means

The kubeadm token-create style command validates its --output flag against a closed set {text, json, yaml}; an empty value defaults to text, anything else is rejected immediately before any token is generated.

Source

Thrown at pkg/kubeadm/token.go:35

// SetDefaults ensures that the default values are set on the token configuration.
// These are set here, rather than in the default Token struct, to avoid
// importing the cluster-bootstrap packages into the CLI.
func SetDefaults(clx *cli.Context, cfg *cmds.Token) error {
	if !clx.IsSet("groups") {
		cfg.Groups = *cli.NewStringSlice(NodeBootstrapTokenAuthGroup)
	}

	if !clx.IsSet("usages") {
		cfg.Usages = *cli.NewStringSlice(bootstrapapi.KnownTokenUsages...)
	}

	if cfg.Output == "" {
		cfg.Output = "text"
	} else {
		switch cfg.Output {
		case "text", "json", "yaml":
		default:
			return errors.New("invalid output format: " + cfg.Output)
		}
	}

	if clx.Args().Len() > 0 {
		cfg.Token = clx.Args().Get(0)
	}

	if cfg.Token == "" {
		var err error
		cfg.Token, err = bootstraputil.GenerateBootstrapToken()
		if err != nil {
			return err
		}
	}

	return nil
}

View on GitHub (pinned to 6ba341e396)

Solutions

1. Use one of: --output=text, --output=json, --output=yaml.
2. Omit --output entirely when plain text is desired (it is the default).
3. Validate the variable before passing it: case "$OUT" in text|json|yaml) ;; *) echo bad ;; esac.

Example fix

# before
k3s token create --output=wide
# after
k3s token create --output=json

switch cfg.Output {
case "", "text", "json", "yaml":
default:
    return fmt.Errorf("invalid output format %q (want text|json|yaml)", cfg.Output)
}

func validOutputFormat(s string) bool {
	switch s {
	case "", "text", "json", "yaml":
		return true
	}
	return false
}

When it happens

Trigger: Running 'k3s token create --output=wide' or --output=table, or piping a script variable that is unset/whitespace into --output.

Common situations: Copy-pasting from kubectl docs where 'wide'/'name' are valid; shell defaults like OUTPUT=${OUTPUT:-table}; YAML templating that injects quotes into the value.

Related errors

• --token is required
• --server is required
• service %s is not recognized
• no snapshots given for removal
• invalid output format:

AI-assisted analysis of k3s-io/k3s@6ba341e396 (2026-08-15). Data as JSON: /api/errors/43fca34e7f075e4b. Report an issue: GitHub.