1. rubygemsのバージョンをアップデートする。

   % sudo gem install rubygems-update
   % sudo gem update rubygems-update
   

2. Railsをインストールする。

   % sudo gem update rails

   MySQLのドライバーがねーよ！とか言われた人はMysqlのドライバーもインストールする。↓

   %sudo apt-get install libmysqlclient15-dev
   %sudo gem install mysql
   

   他にもインストールしたいのあれば参考に→[Ubuntu]Ubuntu8.10へRailsをインストールしたよ。[Rails]

3. 既存のアプリケーションが利用しているRailsのバージョンを上げる。

   % cd /var/www/rails/app  ## Railsアプリケーションまで移動する。移動先は自分の環境に合わせて
   % vi config/environment.rb
   RAILS_GEM_VERSION = '2.1.0'
   ↓ ## 使いたいRailsのバージョンへ修正。
   RAILS_GEM_VERSION = '2.2.2'
   % rake rails:update
   

以上でRailsのバージョンが上がったよと。

% sudo apt-get install ruby ruby-dev irb rubygems libruby-extras libgit-ruby librmagick-ruby vim-ruby vim-rails imagemagick libmagick++9-dev sqlite libsqlite0-dev libsqlite3-dev sqlitebrowser libmysqlclient15-dev  postgresql-server-dev-8.3
% sudo apt-get install lighttpd libfcgi-dev
% sudo gem install rails
% sudo gem install rmagick
% sudo gem install sqlite3-ruby
% sudo gem install mysql
% sudo gem install postgres
% sudo gem install postgres-pr
% sudo gem install vim-ruby
% sudo gem install mongrel
% sudo gem install mongrel_cluster
% sudo gem install fcgi
% sudo gem install net-ssh
% sudo gem install net-sftp
% sudo gem install Selenium
% sudo gem install jpmobile
% sudo gem install ruby-debug
% sudo gem install refe
% sudo gem install xml-simple

※　% sudo gem install xml-simple をインストールのは、Ubuntu8.10で ruby script/generate　とかすると以下のwarningを吐く為。

/usr/lib/ruby/1.8/xmlsimple.rb:275: warning: already initialized constant KNOWN_OPTIONS
/usr/lib/ruby/1.8/xmlsimple.rb:280: warning: already initialized constant DEF_KEY_ATTRIBUTES
/usr/lib/ruby/1.8/xmlsimple.rb:281: warning: already initialized constant DEF_ROOT_NAME
/usr/lib/ruby/1.8/xmlsimple.rb:282: warning: already initialized constant DEF_CONTENT_KEY
/usr/lib/ruby/1.8/xmlsimple.rb:283: warning: already initialized constant DEF_XML_DECLARATION
/usr/lib/ruby/1.8/xmlsimple.rb:284: warning: already initialized constant DEF_ANONYMOUS_TAG
/usr/lib/ruby/1.8/xmlsimple.rb:285: warning: already initialized constant DEF_FORCE_ARRAY
/usr/lib/ruby/1.8/xmlsimple.rb:286: warning: already initialized constant DEF_INDENTATION
/usr/lib/ruby/1.8/xmlsimple.rb:287: warning: already initialized constant DEF_KEY_TO_SYMBOL

sudo gem install mysql — –with-mysql-dir=/usr/local/mysql

Select which gem to install for your platform (i686-darwin8.11.1)
1. mysql 2.7.3 (mswin32)
2. mysql 2.7.1 (mswin32)
3. mysql 2.7 (ruby)
4. mysql 2.6 (ruby)
5. Skip this gem
6. Cancel installation
> Building native extensions. This could take a while…
ERROR: While executing gem … (Gem::Installer::ExtensionBuildError)
ERROR: Failed to build gem native extension.

ruby extconf.rb install mysql — –with-mysql-dir=/usr/local/mysql
checking for mysql_query() in -lmysqlclient… yes
checking for mysql_ssl_set()… yes
checking for mysql.h… yes
creating Makefile

make
gcc -I. -I. -I/opt/local/lib/ruby/1.8/i686-darwin8.11.1 -I. -DHAVE_MYSQL_SSL_SET -DHAVE_MYSQL_H -I/usr/local/mysql/include -I/opt/local/include -fno-common -O2 -fno-common -pipe -fno-common -c mysql.c
mysql.c: In function ‘query’:
mysql.c:635: error: invalid storage class for function ‘res_free’
mysql.c:637: error: ‘res_free’ undeclared (first use in this function)
mysql.c:637: error: (Each undeclared identifier is reported only once
mysql.c:637: error: for each function it appears in.)
mysql.c: In function ‘Init_mysql’:
mysql.c:1299: error: ‘ulong’ undeclared (first use in this function)
mysql.c:1299: error: parse error before numeric constant
mysql.c:1302: error: parse error before numeric constant
make: *** [mysql.o] Error 1

Gem files will remain installed in /opt/local/lib/ruby/gems/1.8/gems/mysql-2.7 for inspection.
Results logged to /opt/local/lib/ruby/gems/1.8/gems/mysql-2.7/gem_make.out

と、エラーを吐く。
以下、解決法↓

sudo vim /opt/local/lib/ruby/gems/1.8/gems/mysql-2.7/mysql.c.in.
ファイル先頭に
#define ulong unsigned long
と記述。

cd /opt/local/lib/ruby/gems/1.8/gems/mysql-2.7
sudo ruby extconf.rb –with-mysql-config=/usr/local/mysql/bin/mysql_config
sudo make
sudo make install

以上。メモ。