fluent/fluentd · error · Fluent::ConfigError

sd_file: path=#{@path} couldn't open #{e}

Error message

sd_file: path=#{@path} couldn't open #{e}

What it means

SdFileServiceDiscovery#fetch_server_info (lib/fluent/plugin/sd_file.rb:121) opens the services file with File.open(path, 'r:{conf_encoding}:utf-8') and wraps any exception in Fluent::ConfigError. Unlike the not-found case (error 236), this fires when the file exists but cannot be read or decoded: permission denied, encoding name typos, or content that cannot be converted from conf_encoding to UTF-8.

Source

Thrown at lib/fluent/plugin/sd_file.rb:121

        drain = @services - s
        drain.each do |d|
          diff << ServiceDiscovery.service_out_msg(d)
        end

        @services = s

        diff.each do |a|
          queue.push(a)
        end
      end

      def fetch_server_info
        config_data =
          begin
            File.open(@path, "r:#{@conf_encoding}:utf-8", &:read)
          rescue => e
            raise Fluent::ConfigError, "sd_file: path=#{@path} couldn't open #{e}"
          end

        parser.call(config_data).map do |s|
          Service.new(
            :file,
            s.fetch('host'),
            s.fetch('port'),
            s['name'],
            s.fetch('weight', DEFAULT_WEIGHT),
            s['standby'],
            s['username'],
            s['password'],
            s['shared_key'],
          )
        end
      rescue KeyError => e
        raise Fluent::ConfigError, "#{e}. Service must have `host` and `port`"
      end

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Fix permissions: chown fluent:fluent /etc/fluent/services.yaml or chmod a+r (as appropriate).
2. Set conf_encoding to the file's real Ruby encoding name (<service_discovery> @type file path ... conf_encoding SJIS </service_discovery>).
3. Re-save the services file as UTF-8 and drop conf_encoding.
4. Verify readability as the fluentd user: sudo -u fluent head -1 /etc/fluent/services.yaml.

Example fix

# before
<service_discovery>
  @type file
  path /etc/fluent/servers.yaml
  conf_encoding utf8       # invalid encoding name
</service_discovery>
# after
<service_discovery>
  @type file
  path /etc/fluent/servers.yaml
  conf_encoding UTF-8
</service_discovery>

# pre-start readability + encoding probe
enc = 'UTF-8'
data = File.read(path, encoding: "#{enc}:utf-8") # raises here if unreadable/undecodable

When it happens

Trigger: File mode 0600 owned by another user while fluentd runs unprivileged; conf_encoding set to 'utf8' (must be a Ruby encoding name like 'UTF-8' or 'EUC-JP'); a Shift_JIS/EUC-KR file declared as UTF-8 causing an UndefinedConversionError during read.

Common situations: Running fluentd as the 'fluent' user on files created by root; Japanese/Korean legacy-encoded service lists; Docker volume mounts that preserve restrictive permissions; copy-pasted conf_encoding values from examples using non-Ruby names.

Related errors

• sd_file: path=#{@path} not found
• #{e}. Service must have `host` and `port`
• e.message
• unknown value conversion for key:'#{field_name}', type:'#{ty
• Invalid regexp '#{formats}': #{e}

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/78f1ea9e39bd9c8a. Report an issue: GitHub.