我能并排安装RubyonRails2.x和RubyonRails3吗

this railscast 更多信息。这允许您在同一台机器上轻松地管理不同版本的Ruby。我相信这也应该使您能够保持不同版本的Rails彼此独立,并允许您轻松地在它们之间进行切换—请参见下面的示例 http://rvm.beginrescueend.com/gemsets/basics/ :

rvm 1.9.2-head
gem install rails -v 2.3.3

rvm gemset create rails222 rails126
Gemset 'rails222' created.
Gemset 'rails126' created.

rvm 1.9.2-head@rails222
gem install rails -v 2.2.2

rvm 1.9.2-head@rails126
gem install rails -v 1.2.6

为了 窗户

(我知道asker使用的是Ubuntu,但当我有一个与Windows相关的问题时,SERPs中出现了这个问题。)

可以 pik

-- install the gem    
> gem install pik

-- run 'install' command to add the utility to your system
> pik_install [some dir in your PATH variable]

-- tell pik where your Ruby versions are
> pik add C:\Ruby187\bin
> pik add C:\Ruby193\bin

-- see which versions pik has under control and which one is actively being used
> pik list
* 187: ruby 1.8.7 (2011-06-30 patchlevel 352) [i386-mingw32]
  193: ruby 1.9.3p194 (2012-04-20) [i386-mingw32]

-- tell pik to use a different version
> pik use 193
> pik list
  187: ruby 1.8.7 (2011-06-30 patchlevel 352) [i386-mingw32]
* 193: ruby 1.9.3p194 (2012-04-20) [i386-mingw32]

-- confirm the change worked:
> ruby -v && rails -v
ruby 1.9.3p194 (2012-04-20) [i386-mingw32]
Rails 3.2.3