I recommend to go straight to 2.1.5+ without intermediate steps. Otherwhise you burden yourself with unnecessary work of encoding problems.

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

Issues you may encounter:

• Set the ruby version within your .ruby-version file to 2.1.5

• Remove gem ruby-debug and use e.g. byebug

• Remove gem oniguruma

• Remove gem fastercsv

• Replace gem mysql with mysql2

• Update gem capistrano 2.12.0 to ~>2.12 when bound for Ruby 1.8.7 and remove obsolete explicite Gemfile entries for net-scp and net-ssh if present.

• Update gem andand

• Update gem parallel_tests (0.8.x to 1.6.x)

• Downdgrade database_cleaner from 1.4.x to 1.2.0

• Use new lambda syntax: change lambda { |param| code } to ->(param) { code }

• Unbind gem 'i18n', '~> 0.6.0' and update

• fix yml erros:

  • %{count} errors by surrounding with ", e.g.: replace one: %{count} Objekt with one: "%{count} Objekte"

  • date: order: [ :day, :month, :year ] to

    date:
      order:
        - :year
        - :month
        - :day
    

• fix incompatible character encodings: UTF-8 and ASCII-8BIT error by adding

  Encoding.default_external = Encoding::UTF_8
  Encoding.default_internal = Encoding::UTF_8
  

  to environment.rb before Appname::Application.initialize!

• use ' ' for nbsp helper instead of 0xC2.chr + 0xA0.chr

• TextHelper#truncate changed signature from (string, int) to (string, length: int)

• You may update gem sanitize from 2.x to 4+

• In regexes \w does not match umlauts and other special characters. If it is supposed to you can use [[:alnum:]] instead.