What causes "Section %{name} is already defined, cannot redefine" in puppetlabs/puppet?

De-duplicate the section headers in the file: merge the key/value pairs of the repeats into a single block

puppetlabs/puppet · error · Puppet::Util::IniConfig::IniParseError

Section %{name} is already defined, cannot redefine

Error message

Section %{name} is already defined, cannot redefine

What it means

IniFile#add_section raises IniParseError when a section with that name already exists (section_exists? found it via get_section). Crucially, #parse itself calls add_section for every [name] header, so an INI file containing the same section header twice fails with this error at read time. Puppet deliberately refuses to silently merge duplicate sections.

Source

Thrown at lib/puppet/util/inifile.rb:242

    def store
      if @destroy_empty and (sections.empty? or sections.all?(&:destroy?))
        ::File.unlink(@file)
      elsif sections.any?(&:dirty?)
        text = self.format
        @filetype.write(text)
      end
      sections.each(&:mark_clean)
    end

    # Create a new section and store it in the file contents
    #
    # @api private
    # @param name [String] The name of the section to create
    # @return [Puppet::Util::IniConfig::Section]
    def add_section(name)
      if section_exists?(name)
        raise IniParseError.new(_("Section %{name} is already defined, cannot redefine") % { name: name.inspect }, @file)
      end

      section = Section.new(name, @file)
      @contents << section

      section
    end

    private

    def section_exists?(name)
      if get_section(name)
        true
      elsif @file_collection and @file_collection.get_section(name)
        true
      else
        false
      end

View on GitHub (pinned to e227c27540)

Solutions

De-duplicate the section headers in the file: merge the key/value pairs of the repeats into a single block
In code, guard the call: only add_section when ini.sections has no section with that name
Use the existing section instead of adding: fetch it from ini.sections and mutate its entries
Rescue IniParseError when section names come from untrusted input; the error carries @file for reporting

Example fix

# before
ini.add_section('agent')  # IniParseError if [agent] already present

# after
section = ini.sections.find { |s| s.name == 'agent' } || ini.add_section('agent')
section['server'] = 'puppet.example.com'

Defensive patterns

Strategy: validation

Validate before calling

unless ini.sections.any? { |s| s.name == wanted }
  ini.add_section(wanted)
end

Try / catch

begin
  ini.add_section(name)
rescue Puppet::Util::IniConfig::IniParseError
  ini.sections.find { |s| s.name == name } # already exists: reuse it
end

Prevention

Treat add_section as create-only; fetch-or-create via ini.sections lookup instead
Deduplicate section headers when merging INI files (check for repeats before writing)
Run idempotent config scripts that check current state before mutating

When it happens

Trigger: Reading an INI file with duplicated headers (two [main] blocks); calling ini_file.add_section('agent') when the file's sections already include one named 'agent'; appends (cat a >> b) producing repeated headers.

Common situations: Hand-merged puppet.conf-style files keeping both copies of a section; deployment scripts that unconditionally add a section on every run; configuration templates instantiated twice into one file.

Related errors

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/512cdb08193a53fa. Report an issue: GitHub.