fluent/fluentd · error · ConfigError

valid options are #{list.join(',')} but got #{val}

Error message

valid options are #{list.join(',')} but got #{val}

What it means

For enum parameters (config_param :x, :enum, list: [:a, :b]), enum_value converts the value to a Symbol and checks membership in the plugin-provided :list; a miss raises ConfigError with the exact allowed set in the message. The check runs only after verifying the plugin itself supplied a Symbol array, otherwise the author-facing 'Plugin BUG' error fires first. Comparison is exact and case-sensitive after to_sym, so 'JSON' will not match :json.

Source

Thrown at lib/fluent/config/types.rb:128

    def self.symbol_value(val, opts = {}, name = nil)
      return nil if val.nil? || val.empty?

      val.delete_prefix(":").to_sym
    end

    SYMBOL_TYPE = Proc.new { |val, opts = {}, name = nil|
      Config.symbol_value(val, opts, name)
    }

    def self.enum_value(val, opts = {}, name = nil)
      return nil if val.nil?

      s = val.to_sym
      list = opts[:list]
      raise "Plugin BUG: config type 'enum' requires :list of symbols" unless list.is_a?(Array) && list.all?(Symbol)
      unless list.include?(s)
        raise ConfigError, "valid options are #{list.join(',')} but got #{val}"
      end
      s
    end

    ENUM_TYPE = Proc.new { |val, opts = {}, name = nil|
      Config.enum_value(val, opts, name)
    }

    INTEGER_TYPE = Proc.new { |val, opts = {}, name = nil|
      if val.nil?
        nil
      elsif opts[:strict]
        begin
          Integer(val)
        rescue ArgumentError, TypeError => e
          raise ConfigError, "#{name}: #{e.message}"
        end
      else

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Use one of the values printed in the error message (they are the plugin's declared list)
2. Fix typos and casing — the value must match a listed symbol exactly
3. Check the plugin's docs/config_param declaration for the current allowed set; plugin versions sometimes narrow the list
4. If you own the plugin, add the value to the :list or switch the param to :string when an open-ended value is legitimate

Example fix

# before
# config_param :format, :enum, list: [:out_file, :json, :ltsv]
<match demo.**>
  @type file
  <format>
    @type ltsvv
  </format>
</match>

# after
<match demo.**>
  @type file
  <format>
    @type ltsv
  </format>
</match>

allowed = %i[text json ltsv] # from the plugin's :list
unless allowed.include?(raw_value.to_sym)
  raise ArgumentError, "#{raw_value.inspect} not in #{allowed.join(',')}"
end

When it happens

Trigger: config_param :format, :enum, list: [:text, :ltsv] with 'format json' (json not in list), a typo like 'jsonn', wrong casing, or an ENV-expanded value that yields a string outside the declared list.

Common situations: Copy-pasting a value valid for a different plugin (e.g. 'json' where the plugin only accepts :msgpack/:text); typos in long option names; case-mismatched values; upgrading a plugin whose enum list dropped an old value.

Related errors

• Unknown #{@kind} plugin '#{type}'. Run 'gem search -rd fluen
• Missing '@type' parameter on <#{e.name}> directive
• 'format' parameter is required
• both of utc and localtime are specified, use only one of the
• this plugin '#{self.class}' cannot handle arguments for <buf

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/409282d51d688d02. Report an issue: GitHub.