fluent/fluentd · error · Fluent::ConfigError

e.message

Error message

e.message

What it means

in_exec's optional encoding param is validated by Encoding.find(encoding); Ruby raises ArgumentError for any name that does not map to a registered encoding (e.g. 'unknown encoding name - utf88'), and validate_encoding re-raises that message verbatim as Fluent::ConfigError. The value becomes the external encoding of the spawned command's stdin/stdout pipes, so it must be a real Ruby encoding name (UTF-8, EUC-JP, Windows-31J, ...).

Source

Thrown at lib/fluent/plugin/in_exec.rb:77

          if subsection.has_key?('time_format')
            subsection['time_type'] ||= 'string'
          end
        end
      end

      super

      if !@tag && (!@extract_config || !@extract_config.tag_key)
        raise Fluent::ConfigError, "'tag' or 'tag_key' option is required on exec input"
      end
      validate_encoding(@encoding) if @encoding
      @parser = parser_create
    end

    def validate_encoding(encoding)
      Encoding.find(encoding)
    rescue ArgumentError => e
      raise Fluent::ConfigError, e.message
    end

    def multi_workers_ready?
      true
    end

    def start
      super

      options = { mode: [@connect_mode] }
      options[:external_encoding] = @encoding if @encoding

      if @run_interval
        child_process_execute(:exec_input, @command, interval: @run_interval, wait_timeout: @command_timeout, **options, &method(:run))
      else
        child_process_execute(:exec_input, @command, immediate: true, wait_timeout: @command_timeout, **options, &method(:run))
      end
    end

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Use a name Ruby's Encoding.find accepts: ruby -e 'puts Encoding.list.map(&:to_s)' to list valid ones.
2. For locale strings, strip to the encoding part only (UTF-8 out of en_US.UTF-8).
3. Run fluentd --dry-run to fail fast at config load rather than at runtime.

Example fix

# before
<source>
  @type exec
  command /opt/scripts/dump.sh
  encoding en_US.UTF-8
</source>
# after
<source>
  @type exec
  command /opt/scripts/dump.sh
  encoding UTF-8
</source>

# preflight: validate the encoding name exactly as in_exec will
Encoding.find('UTF-8') # raises ArgumentError for invalid names
# programmatic check for a config value:
begin
  Encoding.find(candidate_encoding)
rescue ArgumentError
  abort "invalid encoding for in_exec: #{candidate_encoding}"
end

->(name) { name.is_a?(String) && (Encoding.find(name) rescue nil) }

begin
  Fluent::Plugin.new_input('exec').configure(conf)
rescue Fluent::ConfigError => e
  abort "exec input config rejected: #{e.message}" # e.g. 'unknown encoding name - en_US.UTF-8'
end

When it happens

Trigger: Setting encoding to a locale-style string ('en_US.UTF-8'), a typo ('utf8x', 'UTF--8'), or an unregistered alias in an in_exec source; the ArgumentError message from Encoding.find becomes the ConfigError text shown.

Common situations: Copy-pasting locale environment values into encoding; assuming iconv/codepage names ('cp1252' works but 'windows-1252x' style typos do not); command output in a legacy Japanese encoding configured with a wrong alias.

Related errors

• 'tag' or 'tag_key' option is required on exec input
• Duplicate key in <or>: #{e.key}
• `renew_record` must be true to use `keep_keys`
• empty value is specified in fields parameter
• unknown_key

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/5c0d15d7daa4e580. Report an issue: GitHub.