fluent/fluentd · error · ArgumentError

Unknown Fluentd configuration syntax: '#{syntax}'

Error message

Unknown Fluentd configuration syntax: '#{syntax}'

What it means

Error "Unknown Fluentd configuration syntax: '#{syntax}'" thrown in fluent/fluentd.

Source

Thrown at lib/fluent/config.rb:63

        if additional_config
          c = additional_config.gsub("\\n", "\n")
          s += "\n#{c}"
        end
        s
      end

      Fluent::Config.parse(config_data, config_fname, config_basedir, use_v1_config, on_file_parsed: on_file_parsed)
    end

    def self.parse(str, fname, basepath = Dir.pwd, v1_config = nil, syntax: :v1, on_file_parsed: nil)
      parser = if fname =~ /\.rb$/ || syntax == :ruby
                 :ruby
               elsif v1_config.nil?
                 case syntax
                 when :v1 then :v1
                 when :v0 then :v0
                 else
                   raise ArgumentError, "Unknown Fluentd configuration syntax: '#{syntax}'"
                 end
               elsif v1_config then :v1
               else :v0
               end
      case parser
      when :v1
        require 'fluent/config/v1_parser'
        V1Parser.parse(str, fname, basepath, Kernel.binding, on_file_parsed: on_file_parsed)
      when :v0
        # TODO: show deprecated message in v1
        require 'fluent/config/parser'
        Parser.parse(str, fname, basepath)
      when :ruby
        require 'fluent/config/dsl'
        $log.warn("Ruby DSL configuration format is deprecated. Please use original configuration format. https://docs.fluentd.org/configuration/config-file") if $log
        Config::DSL::Parser.parse(str, File.join(basepath, fname))
      else
        raise "[BUG] unknown configuration parser specification:'#{parser}'"

View on GitHub (pinned to dd45c6e18d)

When it happens

Trigger: Thrown at lib/fluent/config.rb:63 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/c43bec1794264e54. Report an issue: GitHub.