Ubuntu：Ruby と Ruby on Rails のインストール手順（公式ドキュメントベース）

Rubyをイントールします（https://www.ruby-lang.org/en/documentation/installation/#apt）。

$ sudo apt-get install ruby-full

gem も入ります。

$ gem --version
1.8.23

ただ、「ruby 1.9.3p484」という古いものが入ってしまったのですが、Ruby on Rails的には「We recommend Ruby 2.2 or newer for use with Rails.」のようなので、更新します。

まず、gitを準備します。

$ sudo apt-get install git

rbenv を ~/.rbenv に checkout してきます。

$ git clone https://github.com/sstephenson/rbenv.git ~/.rbenv

~/.rbenv/bin を $PATH に追加し、rbenv init を登録します。

$ echo &#039;export PATH=&quot;$HOME/.rbenv/bin:$PATH&quot;&#039; &gt;&gt; ~/.bashrc<br />
echo 'eval "$(rbenv init -)"' >> ~/.bashrc

（~/.bashrc の部分は、適宜変更。zshの場合は ~/.zshrc に。）

シェルを再起動（「$ source ~/.bashrc」でもいいはず）して、「$ type rbenv」を実行して、「rbenv は関数です」と表示されればインストール成功です（「bash: type: rbenv: 見つかりません」と表示されたら失敗しているか、再起動忘れ）。

rbenvプラグインのruby-buildを入れます。

$ git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build

このコマンド一つでインストール完了です。

これで、特定のバージョンのRubyをインストールできます。

まず、インストール可能なバージョンを特定します。

$ rbenv install -l

Available versions:
  1.8.6-p383
  1.8.6-p420
  1.8.7-p249
  1.8.7-p302
  1.8.7-p334
  1.8.7-p352
  1.8.7-p357
  1.8.7-p358
  1.8.7-p370
  1.8.7-p371
  1.8.7-p374
  1.8.7-p375
  1.9.1-p378
  1.9.1-p430
  1.9.2-p0
  1.9.2-p180
  1.9.2-p290
  1.9.2-p318
  1.9.2-p320
  1.9.2-p326
  1.9.2-p330
  1.9.3-dev
  1.9.3-preview1
  1.9.3-rc1
  1.9.3-p0
  1.9.3-p125
  1.9.3-p194
  1.9.3-p286
  1.9.3-p327
  1.9.3-p362
  1.9.3-p374
  1.9.3-p385
  1.9.3-p392
  1.9.3-p429
  1.9.3-p448
  1.9.3-p484
  1.9.3-p545
  1.9.3-p547
  1.9.3-p550
  1.9.3-p551
  2.0.0-dev
  2.0.0-preview1
  2.0.0-preview2
  2.0.0-rc1
  2.0.0-rc2
  2.0.0-p0
  2.0.0-p195
  2.0.0-p247
  2.0.0-p353
  2.0.0-p451
  2.0.0-p481
  2.0.0-p576
  2.0.0-p594
  2.0.0-p598
  2.0.0-p643
  2.0.0-p645
  2.1.0-dev
  2.1.0-preview1
  2.1.0-preview2
  2.1.0-rc1
  2.1.0
  2.1.1
  2.1.2
  2.1.3
  2.1.4
  2.1.5
  2.1.6
  2.2.0-dev
  2.2.0-preview1
  2.2.0-preview2
  2.2.0-rc1
  2.2.0
  2.2.1
  2.2.2
  2.3.0-dev
  jruby-1.5.6
（以降略）

Ruby on Rails では、

We recommend Ruby 2.2 or newer for use with Rails. Rails requires Ruby 1.9.3 or newer. （引用元）

となっているので、1.9.3以降が必須で、2.2以上が推奨されています。

すると、現状では、2.2.0、2.2.1、2.2.2の３択となると思うのですが、ここでは最新の 2.2.2 にしておきます。

$ rbenv install 2.2.2
Downloading ruby-2.2.2.tar.gz...
-> https://dqw8nmjcqpjn7.cloudfront.net/5ffc0f317e429e6b29d4a98ac521c3ce65481bfd22a8cf845fa02a7b113d9b44
Installing ruby-2.2.2...

BUILD FAILED (Ubuntu 14.04 using ruby-build 20150719-7-ge40e84f)

Inspect or clean up the working tree at /tmp/ruby-build.20150722233833.10887
Results logged to /tmp/ruby-build.20150722233833.10887.log

Last 10 log lines:
The Ruby openssl extension was not compiled.
The Ruby readline extension was not compiled.
The Ruby zlib extension was not compiled.
ERROR: Ruby install aborted due to missing extensions
Try running `apt-get install -y libssl-dev libreadline-dev zlib1g-dev` to fetch missing dependencies.

Configure options used:
  --prefix=/home/did2/.rbenv/versions/2.2.2
  LDFLAGS=-L/home/did2/.rbenv/versions/2.2.2/lib 
  CPPFLAGS=-I/home/did2/.rbenv/versions/2.2.2/include 

よく見ると、エラーが出ています。そこで、指示通り、次を実行しました（環境、実行結果によってコマンドが変わります）。

$ sudo apt-get install -y libssl-dev libreadline-dev zlib1g-dev

これを終えた上で、もう一度インストールコマンドを実行した結果がこちらです。

$ rbenv install 2.2.2
Downloading ruby-2.2.2.tar.gz...
-> https://dqw8nmjcqpjn7.cloudfront.net/5ffc0f317e429e6b29d4a98ac521c3ce65481bfd22a8cf845fa02a7b113d9b44
Installing ruby-2.2.2...
Installed ruby-2.2.2 to /home/did2/.rbenv/versions/2.2.2

インストールに成功しました。

「gem」コマンドが使えるはずなので、次のコマンドで、railsをインストールできます（マニュアルのRailsの項）。

gem install rails
Fetching: i18n-0.7.0.gem (100%)
ERROR:  While executing gem ... (Errno::EACCES)
    Permission denied - /var/lib/gems

sudoを忘れました。もう一度実行します。

sudo gem install rails
Fetching: i18n-0.7.0.gem (100%)
ERROR:  While executing gem ... (Errno::EACCES)
    Permission denied - /var/lib/gems
did2@did2-UbuntuDesktopG1:~$ sudo gem install rails
[sudo] password for did2: 
Fetching: i18n-0.7.0.gem (100%)
Fetching: json-1.8.3.gem (100%)
Building native extensions.  This could take a while...
Fetching: thread_safe-0.3.5.gem (100%)
Fetching: tzinfo-1.2.2.gem (100%)
Fetching: minitest-5.7.0.gem (100%)
Fetching: activesupport-4.2.3.gem (100%)
Fetching: rack-1.6.4.gem (100%)
Fetching: rack-test-0.6.3.gem (100%)
Fetching: mini_portile-0.6.2.gem (100%)
Fetching: nokogiri-1.6.6.2.gem (100%)
Building native extensions.  This could take a while...
Fetching: loofah-2.0.2.gem (100%)
Fetching: rails-html-sanitizer-1.0.2.gem (100%)
Fetching: rails-deprecated_sanitizer-1.0.3.gem (100%)
Fetching: rails-dom-testing-1.0.6.gem (100%)
Fetching: builder-3.2.2.gem (100%)
Fetching: erubis-2.7.0.gem (100%)
Fetching: actionview-4.2.3.gem (100%)
Fetching: actionpack-4.2.3.gem (100%)
Fetching: activemodel-4.2.3.gem (100%)
Fetching: arel-6.0.2.gem (100%)
Fetching: activerecord-4.2.3.gem (100%)
Fetching: globalid-0.3.5.gem (100%)
Fetching: activejob-4.2.3.gem (100%)
Fetching: mime-types-2.6.1.gem (100%)
Fetching: mail-2.6.3.gem (100%)
Fetching: actionmailer-4.2.3.gem (100%)
Fetching: rake-10.4.2.gem (100%)
Fetching: thor-0.19.1.gem (100%)
Fetching: railties-4.2.3.gem (100%)
Fetching: bundler-1.10.5.gem (100%)
Fetching: sprockets-3.2.0.gem (100%)
Fetching: sprockets-rails-2.3.2.gem (100%)
Fetching: rails-4.2.3.gem (100%)
Successfully installed i18n-0.7.0
Successfully installed json-1.8.3
Successfully installed thread_safe-0.3.5
Successfully installed tzinfo-1.2.2
Successfully installed minitest-5.7.0
Successfully installed activesupport-4.2.3
Successfully installed rack-1.6.4
Successfully installed rack-test-0.6.3
Successfully installed mini_portile-0.6.2
Successfully installed nokogiri-1.6.6.2
Successfully installed loofah-2.0.2
Successfully installed rails-html-sanitizer-1.0.2
Successfully installed rails-deprecated_sanitizer-1.0.3
Successfully installed rails-dom-testing-1.0.6
Successfully installed builder-3.2.2
Successfully installed erubis-2.7.0
Successfully installed actionview-4.2.3
Successfully installed actionpack-4.2.3
Successfully installed activemodel-4.2.3
Successfully installed arel-6.0.2
Successfully installed activerecord-4.2.3
Successfully installed globalid-0.3.5
Successfully installed activejob-4.2.3
Successfully installed mime-types-2.6.1
Successfully installed mail-2.6.3
Successfully installed actionmailer-4.2.3
Successfully installed rake-10.4.2
Successfully installed thor-0.19.1
Successfully installed railties-4.2.3
Successfully installed bundler-1.10.5
Successfully installed sprockets-3.2.0
Successfully installed sprockets-rails-2.3.2
Successfully installed rails-4.2.3
33 gems installed
Installing ri documentation for i18n-0.7.0...
Installing ri documentation for json-1.8.3...
Installing ri documentation for thread_safe-0.3.5...
Installing ri documentation for tzinfo-1.2.2...
Installing ri documentation for minitest-5.7.0...
Installing ri documentation for activesupport-4.2.3...
Installing ri documentation for rack-1.6.4...
Installing ri documentation for rack-test-0.6.3...
Installing ri documentation for mini_portile-0.6.2...
Installing ri documentation for nokogiri-1.6.6.2...
Installing ri documentation for loofah-2.0.2...
Installing ri documentation for rails-html-sanitizer-1.0.2...
Installing ri documentation for rails-deprecated_sanitizer-1.0.3...
Installing ri documentation for rails-dom-testing-1.0.6...
Installing ri documentation for builder-3.2.2...
Installing ri documentation for erubis-2.7.0...
Installing ri documentation for actionview-4.2.3...
Installing ri documentation for actionpack-4.2.3...
Installing ri documentation for activemodel-4.2.3...
Installing ri documentation for arel-6.0.2...
Installing ri documentation for activerecord-4.2.3...
Installing ri documentation for globalid-0.3.5...
Installing ri documentation for activejob-4.2.3...
Installing ri documentation for mime-types-2.6.1...
Installing ri documentation for mail-2.6.3...
Installing ri documentation for actionmailer-4.2.3...
Installing ri documentation for rake-10.4.2...
Installing ri documentation for thor-0.19.1...
Installing ri documentation for railties-4.2.3...
Installing ri documentation for bundler-1.10.5...
Installing ri documentation for sprockets-3.2.0...
Installing ri documentation for sprockets-rails-2.3.2...
Installing ri documentation for rails-4.2.3...
file 'lib' not found
Installing RDoc documentation for i18n-0.7.0...
Installing RDoc documentation for json-1.8.3...
Installing RDoc documentation for thread_safe-0.3.5...
Installing RDoc documentation for tzinfo-1.2.2...
Installing RDoc documentation for minitest-5.7.0...
Installing RDoc documentation for activesupport-4.2.3...
Installing RDoc documentation for rack-1.6.4...
Installing RDoc documentation for rack-test-0.6.3...
Installing RDoc documentation for mini_portile-0.6.2...
Installing RDoc documentation for nokogiri-1.6.6.2...
Installing RDoc documentation for loofah-2.0.2...
Installing RDoc documentation for rails-html-sanitizer-1.0.2...
Installing RDoc documentation for rails-deprecated_sanitizer-1.0.3...
Installing RDoc documentation for rails-dom-testing-1.0.6...
Installing RDoc documentation for builder-3.2.2...
Installing RDoc documentation for erubis-2.7.0...
Installing RDoc documentation for actionview-4.2.3...
Installing RDoc documentation for actionpack-4.2.3...
Installing RDoc documentation for activemodel-4.2.3...
Installing RDoc documentation for arel-6.0.2...
Installing RDoc documentation for activerecord-4.2.3...
Installing RDoc documentation for globalid-0.3.5...
Installing RDoc documentation for activejob-4.2.3...
Installing RDoc documentation for mime-types-2.6.1...
Installing RDoc documentation for mail-2.6.3...
Installing RDoc documentation for actionmailer-4.2.3...
Installing RDoc documentation for rake-10.4.2...
Installing RDoc documentation for thor-0.19.1...
Installing RDoc documentation for railties-4.2.3...
Installing RDoc documentation for bundler-1.10.5...
Installing RDoc documentation for sprockets-3.2.0...
Installing RDoc documentation for sprockets-rails-2.3.2...
Installing RDoc documentation for rails-4.2.3...
file 'lib' not found

かなり時間がかかりました。

とりあえず気になるのが「file 'lib' not found」です。詳細のわからないエラーメッセージです。

ちなみに、そのままもう一度「sudo gem install rails」すると、次のようになります。

$ sudo gem install rails
[sudo] password for did2: 
Successfully installed rails-4.2.3
1 gem installed
Installing ri documentation for rails-4.2.3...
file 'lib' not found
Installing RDoc documentation for rails-4.2.3...
file 'lib' not found

繰り返されます。

ここで、「installation - rails 3 install error "File not found: lib"」を参考に、「gem install rdoc」を実行してから、もう一度インストールしてみます。

$ sudo gem install rdoc
Fetching: rdoc-4.2.0.gem (100%)
Depending on your version of ruby, you may need to install ruby rdoc/ri data:

<= 1.8.6 : unsupported
 = 1.8.7 : gem install rdoc-data; rdoc-data --install
 = 1.9.1 : gem install rdoc-data; rdoc-data --install
>= 1.9.2 : nothing to do! Yay!
Successfully installed rdoc-4.2.0
1 gem installed
Installing ri documentation for rdoc-4.2.0...
Installing RDoc documentation for rdoc-4.2.0...
(eval):3: warning: string literal in condition
(eval):2: warning: string literal in condition

$ sudo gem install rails
Successfully installed rails-4.2.3
1 gem installed
Installing ri documentation for rails-4.2.3...
Installing RDoc documentation for rails-4.2.3...

これで無事、RubyとRuby on Railsのインストールが終わりました。