Ruby on Rails をインストール

$gem install rails

Fetching: rails-3.2.12.gem (100%)
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions into the /usr/local/lib/ruby/gems/1.9.1 directory.
$sudo /usr/local/bin/gem install rails


Successfully installed rails-3.2.12
1 gem installed
Installing ri documentation for rails-3.2.12...
Installing RDoc documentation for rails-3.2.12...


$ gem which rails
/usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails.rb

$ rails -v
Rails 3.2.12
$rails new AppName
#AppNameが作成される
cd AppName
#動かしてみる
$rails start

/usr/local/lib/ruby/gems/1.9.1/gems/execjs-1.4.0/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
from /usr/local/lib/ruby/gems/1.9.1/gems/execjs-1.4.0/lib/execjs.rb:5:in `<module:ExecJS>'
from /usr/local/lib/ruby/gems/1.9.1/gems/execjs-1.4.0/lib/execjs.rb:4:in `<top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-script-2.2.0/lib/coffee_script.rb:1:in `<top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-script-2.2.0/lib/coffee-script.rb:1:in `<top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/coffee-rails-3.2.2/lib/coffee-rails.rb:1:in `<top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:72:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:72:in `block (2 levels) in require'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:70:in `each'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:70:in `block in require'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:59:in `each'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler/runtime.rb:59:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/bundler-1.3.0/lib/bundler.rb:132:in `require'
from /home/yoshioka/myBooks/config/application.rb:7:in `<top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:53:in `require'
from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:53:in `block in <top (required)>'
from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `tap'
from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
#エラー。。
#autodetect が見つからない？
#https://github.com/sstephenson/execjs を見てみる
#README.md

Installation

$ gem install execjs

#試してみる
$gem install execjs
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions into the /usr/local/lib/ruby/gems/1.9.1 directory.

$sudo /usr/local/bin/gem install execjs

Successfully installed execjs-1.4.0
1 gem installed
Installing ri documentation for execjs-1.4.0...
Installing RDoc documentation for execjs-1.4.0...
#もう一度実行してみる
$rails server
/usr/local/lib/ruby/gems/1.9.1/gems/execjs-1.4.0/lib/execjs/runtimes.rb:51:in `autodetect': Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)
#同じエラー
#Gemfileを編集した。

$ diff Gemfile Gemfile.20130309
18c18
<    gem 'therubyracer', :platforms => :ruby
---
>   # gem 'therubyracer', :platforms => :ruby






#再度実行

$ rails server
=> Booting WEBrick
=> Rails 3.2.12 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2013-03-09 11:41:51] INFO  WEBrick 1.3.1
[2013-03-09 11:41:51] INFO  ruby 1.9.3 (2011-10-30) [x86_64-linux]
[2013-03-09 11:41:51] INFO  WEBrick::HTTPServer#start: pid=5481 port=3000
#動いた