Rails 3.0.0.beta安装问题：找不到可执行的rails

我正在尝试安装rails 3.0.0.beta，我遇到了这个问题：

justins-mac-: justinz$ ruby -v ruby 1.8.7 (2008-08-11 patchlevel 72) [universal-darwin10.0] justins-mac-justinz$ rails -help /Library/Ruby/Site/1.8/rubygems.rb:384:in `bin_path': can't find executable rails for rails-3.0.0.beta (Gem::Exception) from /usr/bin/rails:19 justins-mac-justinz$ rails -v /Library/Ruby/Site/1.8/rubygems.rb:384:in `bin_path': can't find executable rails for rails-3.0.0.beta (Gem::Exception) from /usr/bin/rails:19 justins-mac-justinz$ 

关于这里发生了什么的任何线索？

Answer 1

升级rubygems并清理后，您需要：

 gem install railties --pre 

Answer 2

 sudo gem install railties --pre 

Answer 3

尝试

 sudo gem update --system 

既然什么也没做，试试吧

 sudo gem cleanup 

然后重新安装。