fluent/fluentd · error · Fluent::ConfigError

basename should not include `/`

Error message

basename should not include `/`

What it means

SecondaryFileOutput#configure rejects a `basename` containing `/` (Fluent::ConfigError at configure time). The plugin joins directory + basename into the output path, and a slash inside basename would smuggle extra path components into the file name (ambiguity and escape from the intended directory), so the path structure must be expressed entirely via the `directory` param.

Source

Thrown at lib/fluent/plugin/out_secondary_file.rb:44

    PLACEHOLDER_REGEX = /\${(tag(\[\d+\])?|[\w.@-]+)}/

    desc "The directory path of the output file."
    config_param :directory, :string
    desc "The basename of the output file."
    config_param :basename, :string, default: "dump.bin"
    desc "The flushed chunk is appended to existence file or not."
    config_param :append, :bool, default: false
    config_param :compress, :enum, list: [:text, :gzip], default: :text

    def configure(conf)
      super

      unless @as_secondary
        raise Fluent::ConfigError, "This plugin can only be used in the <secondary> section"
      end

      if @basename.include?("/")
        raise Fluent::ConfigError, "basename should not include `/`"
      end

      @path_without_suffix = File.join(@directory, @basename)
      validate_compatible_with_primary_buffer!(@path_without_suffix)

      @suffix = case @compress
                when :text
                  ""
                when :gzip
                  ".gz"
                end

      test_path = @path_without_suffix
      unless Fluent::FileUtil.writable_p?(test_path)
        raise Fluent::ConfigError, "out_secondary_file: `#{@directory}` should be writable"
      end

      @dir_perm = system_config.dir_permission || Fluent::DEFAULT_DIR_PERMISSION

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Move all directory parts into `directory`: `directory /var/log/fluent/dump/2024` + `basename daily.dump`
2. For dynamic subdirectories, use placeholders on `directory` matched to the primary buffer's chunk keys (e.g. `<buffer time>` + directory `/var/log/dump/%Y%m%d`)
3. Re-check with `fluentd --dry-run`

Example fix

# before
directory /var/log/fluent/buffer
basename dump/2024/daily.bin

# after
directory /var/log/fluent/buffer/2024
basename daily.bin

basename = conf['basename'] || 'dump.bin'
raise "basename must not contain '/': #{basename}" if basename.include?('/')
# put path components only in directory:
directory = conf['directory'] or raise 'directory is required'

When it happens

Trigger: `basename 2024/daily.dump` or `basename backups/dump.bin` — any forward slash in the value. Backslashes are not checked, but on Linux they are legal filename characters, not separators.

Common situations: Trying to add date-partitioned subdirectories via basename instead of directory; migrating a template like path/to/file from @type file (where path accepts slashes) to secondary_file's directory/basename split.

Related errors

• This plugin can only be used in the <secondary> section
• out_secondary_file: `#{@directory}` should be writable
• out_secondary_file: basename or directory has an incompatibl
• out_secondary_file: basename or directory has an incompatibl
• out_secondary_file: basename or directory has an incompatibl

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/1acae4466e2d82c5. Report an issue: GitHub.