我最近更新了Mountain Lion并重新安装了Ruby，但是当我尝试运行测试Rails应用程序时，我收到一条错误消息，指出我的系统上“当前未安装Rails”。我按照它说的做，键入sudo gem install rails并获取：
cleared faster_require caches due to new gem install...
Successfully installed rails-3.2.7
1 gem installed
Installing ri documentation for rails-3.2.7...
Installing RDoc documentation for rails-3.2.7...
但是当我检查安装哪个rails版本时，我得到的是：
Rails is not currently installed on this system. To get the latest version, simply type:
$ sudo gem install rails
You can then rerun your "rails" command.
我也试过gem install rails并获得：
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/Users/aileen/.rvm/rubies/ruby-1.9.3-p194/bin/ruby extconf.rb
creating Makefile
make
compiling generator.c
make: /usr/bin/gcc-4.2: No such file or directory
make: *** [generator.o] Error 1
Gem files will remain installed in /Users/aileen/.rvm/gems/ruby-1.9.3-p194@rails327/gems/json-1.7.4 for inspection.
Results logged to /Users/aileen/.rvm/gems/ruby-1.9.3-p194@rails327/gems/json-1.7.4/ext/json/ext/generator/gem_make.out
答案 0 :(得分：40)
我发现你在 OS X 10.8.2（Mountain lion）上使用 rvm ruby 1.9.3 rails引用的一些宝石可能需要 / usr / bin 中的 gcc-4.2 来构建本机扩展。
在Mountain Lion中，即使安装了 Xcode 4.5 CLI工具（打开菜单XCode - Preferences..Download - ＆gt;命令行工具），您也可以获得 / usr / bin / gcc < / strong>但不是 /usr/bin/gcc-4.2 ;不幸的是某些原生扩展的构建过程依赖于/usr/bin/gcc-4.2
但是我只是在你的环境中顺利安装了导轨。 我之前修改了Carina C. Zona的博客文章Fix for “make: /usr/bin/gcc-4.2: No such file or directory”中所讨论的环境，即：
确保您已安装Homebrew
brew --version
应报告0.9.3或更高
brew更新
现在你可以安装gcc-4.2并创建一个符号链接，这个链接在构建系统中被认为是
brew tap homebrew / dupes
brew install apple-gcc42
sudo ln -s /usr/local/bin/gcc-4.2 /usr/bin/gcc-4.2
现在您已准备好成功安装rails
gem install rails
你应该得到像这样的输出
Fetching: i18n-0.6.1.gem (100%) Fetching: activesupport-3.2.8.gem (100%) Fetching: builder-3.0.4.gem (100%) Fetching: activemodel-3.2.8.gem (100%) Fetching: rack-cache-1.2.gem (100%) Fetching: rack-test-0.6.2.gem (100%) Fetching: journey-1.0.4.gem (100%) Fetching: hike-1.2.1.gem (100%) Fetching: sprockets-2.1.3.gem (100%) Fetching: erubis-2.7.0.gem (100%) Fetching: actionpack-3.2.8.gem (100%) Fetching: arel-3.0.2.gem (100%) Fetching: tzinfo-0.3.34.gem (100%) Fetching: activerecord-3.2.8.gem (100%) Fetching: activeresource-3.2.8.gem (100%) Fetching: polyglot-0.3.3.gem (100%) Fetching: treetop-1.4.12.gem (100%) Fetching: mail-2.4.4.gem (100%) Fetching: actionmailer-3.2.8.gem (100%) Fetching: rack-ssl-1.3.2.gem (100%) Fetching: railties-3.2.8.gem (100%) Fetching: rails-3.2.8.gem (100%) Successfully installed i18n-0.6.1 Successfully installed activesupport-3.2.8 Successfully installed builder-3.0.4 Successfully installed activemodel-3.2.8 Successfully installed rack-cache-1.2 Successfully installed rack-test-0.6.2 Successfully installed journey-1.0.4 Successfully installed hike-1.2.1 Successfully installed sprockets-2.1.3 Successfully installed erubis-2.7.0 Successfully installed actionpack-3.2.8 Successfully installed arel-3.0.2 Successfully installed tzinfo-0.3.34 Successfully installed activerecord-3.2.8 Successfully installed activeresource-3.2.8 Successfully installed polyglot-0.3.3 Successfully installed treetop-1.4.12 Successfully installed mail-2.4.4 Successfully installed actionmailer-3.2.8 Successfully installed rack-ssl-1.3.2 Successfully installed railties-3.2.8 Successfully installed rails-3.2.8 22 gems installed Installing ri documentation for i18n-0.6.1... Building YARD (yri) index for i18n-0.6.1... Installing ri documentation for activesupport-3.2.8... Building YARD (yri) index for activesupport-3.2.8... Installing ri documentation for builder-3.0.4... Building YARD (yri) index for builder-3.0.4... Installing ri documentation for activemodel-3.2.8... Building YARD (yri) index for activemodel-3.2.8... Installing ri documentation for rack-cache-1.2... Building YARD (yri) index for rack-cache-1.2... Installing ri documentation for rack-test-0.6.2... Building YARD (yri) index for rack-test-0.6.2... Installing ri documentation for journey-1.0.4... Building YARD (yri) index for journey-1.0.4... Installing ri documentation for hike-1.2.1... Building YARD (yri) index for hike-1.2.1... Installing ri documentation for sprockets-2.1.3... Building YARD (yri) index for sprockets-2.1.3... Installing ri documentation for erubis-2.7.0... Building YARD (yri) index for erubis-2.7.0... Installing ri documentation for actionpack-3.2.8... Building YARD (yri) index for actionpack-3.2.8... Installing ri documentation for arel-3.0.2... Building YARD (yri) index for arel-3.0.2... Installing ri documentation for tzinfo-0.3.34... Building YARD (yri) index for tzinfo-0.3.34... Installing ri documentation for activerecord-3.2.8... Building YARD (yri) index for activerecord-3.2.8... Installing ri documentation for activeresource-3.2.8... Building YARD (yri) index for activeresource-3.2.8... Installing ri documentation for polyglot-0.3.3... Building YARD (yri) index for polyglot-0.3.3... Installing ri documentation for treetop-1.4.12... Building YARD (yri) index for treetop-1.4.12... Installing ri documentation for mail-2.4.4... Building YARD (yri) index for mail-2.4.4... Installing ri documentation for actionmailer-3.2.8... Building YARD (yri) index for actionmailer-3.2.8... Installing ri documentation for rack-ssl-1.3.2... Building YARD (yri) index for rack-ssl-1.3.2... Installing ri documentation for railties-3.2.8... Building YARD (yri) index for railties-3.2.8... Installing ri documentation for rails-3.2.8... Building YARD (yri) index for rails-3.2.8... Installing RDoc documentation for i18n-0.6.1... Installing RDoc documentation for activesupport-3.2.8... Installing RDoc documentation for builder-3.0.4... Installing RDoc documentation for activemodel-3.2.8... Installing RDoc documentation for rack-cache-1.2... Installing RDoc documentation for rack-test-0.6.2... Installing RDoc documentation for journey-1.0.4... Installing RDoc documentation for hike-1.2.1... Installing RDoc documentation for sprockets-2.1.3... Installing RDoc documentation for erubis-2.7.0... Installing RDoc documentation for actionpack-3.2.8... Installing RDoc documentation for arel-3.0.2... Installing RDoc documentation for tzinfo-0.3.34... Installing RDoc documentation for activerecord-3.2.8... Installing RDoc documentation for activeresource-3.2.8... Installing RDoc documentation for polyglot-0.3.3... Installing RDoc documentation for treetop-1.4.12... Installing RDoc documentation for mail-2.4.4... Installing RDoc documentation for actionmailer-3.2.8... Installing RDoc documentation for rack-ssl-1.3.2... Installing RDoc documentation for railties-3.2.8... Installing RDoc documentation for rails-3.2.8...
答案 1 :(得分：9)
@Franco是正确的：“原生扩展”构建脚本期望/usr/bin/gcc-4.2，这在OS X Mountain Lion中不存在。
sudo ln -s /usr/bin/gcc /usr/bin/gcc-4.2 这不是特定的“rails”宝石问题。任何构建“原生扩展”的gem都会失败：
Gem :: Installer :: ExtensionBuildError：错误：无法构建gem原生扩展。 [...] 您必须先安装开发工具。
在我的情况下，我试图安装install gcc，这取决于名为RedCloth的东西。
答案 2 :(得分：4)
我也和Mountain Lion一起讨论了这个问题。安装失败的宝石是json。为了解决这个问题，我安装了xcode CLI工具，然后将已安装的gcc（i686-apple-darwin11-llvm-gcc-4.2）符号链接为/usr/bin/gcc-4.2。一旦完成，它就会起作用。
在尝试安装另一个gem时，我遇到了类似的问题，其中本机构建步骤抱怨缺少g ++ - 4.2。我用上面的gcc-4.2完全相同，并且它有效。
使用最新的OSX 10.9和最新的RVM，这些问题似乎已经消失。所以，升级的时间。
答案 3 :(得分：3)