[ERROR] /usr/local/lib/ruby/1.9.1/webrick/utils.rb:73:in `initialize': Address already in use - bind(2) (Errno::EADDRINUSE)

"rails s" コマンドを実行すると以下のエラーが出た.
どうやら、既に起動してるみたい...

=> Booting WEBrick
=> Rails 3.2.1 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2012-03-08 10:25:27] INFO  WEBrick 1.3.1
[2012-03-08 10:25:27] INFO  ruby 1.9.2 (2010-12-25) [i686-linux]
[2012-03-08 10:25:27] WARN  TCPServer Error: Address already in use - bind(2)
Exiting
/usr/local/lib/ruby/1.9.1/webrick/utils.rb:73:in `initialize': Address already in use - bind(2) (Errno::EADDRINUSE)
        from /usr/local/lib/ruby/1.9.1/webrick/utils.rb:73:in `new'
        from /usr/local/lib/ruby/1.9.1/webrick/utils.rb:73:in `block in create_listeners'
        from /usr/local/lib/ruby/1.9.1/webrick/utils.rb:70:in `each'
        from /usr/local/lib/ruby/1.9.1/webrick/utils.rb:70:in `create_listeners'
        from /usr/local/lib/ruby/1.9.1/webrick/server.rb:74:in `listen'
        from /usr/local/lib/ruby/1.9.1/webrick/server.rb:62:in `initialize'
        from /usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:24:in `initialize'
        from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/handler/webrick.rb:10:in `new'
        from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/handler/webrick.rb:10:in `run'
        from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/server.rb:265:in `start'
        from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands/server.rb:70:in `start'
        from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands.rb:55:in `block in '
        from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands.rb:50:in `tap'
        from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.1/lib/rails/commands.rb:50:in `'
        from script/rails:6:in `require'
        from script/rails:6:in `
'

対処

既に起動してるプロセスを切ればいいので以下のコマンドで確認

# netstat -anp

Proto...tcp, Program name...ruby の行を発見！ PID より "kill "する.

参考サイト

CentOS5 不要なサービスの停止 - itochif.com

[ERROR] "Session contains objects whose class definition isn't available. Remember to require the classes for all objects kept in the session"

エラーメッセージ

Session contains objects whose class definition isn't available.
Remember to require the classes for all objects kept in the session.
(Original exception: uninitialized constant MySQL [NameError])

対応

古いセッション（ブラウザのクッキー）を削除.

参考サイト

RAILS :“session contains objects whose class definition isn\'t available.”
セッションから復元できないモデルオブジェクトに対処する

ERROR "incompatible character encodings: UTF-8 and ASCII-8BIT"

Rails 3.0 → 3.2 へソースを移行後に下のエラーメッセージが表示された。

ActionView::Template::Error (incompatible character encodings: UTF-8 and ASCII-8BIT):

対応

- Make sure 'config.encoding = "utf-8"' is there in application.rb file.
- Make sure you are using 'mysql2' gem
- Putting '# encoding: utf-8' on top of file containing utf-8 characters.
- Above '::Application.initialize!' line in environment.rb file, add following two lines:

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

参考サイト

Ruby on Rails 3, incompatible character encodings: UTF-8 and ASCII-8BIT with i18n