我刚刚清理了 rvm 和 ruby 并重新安装了它。我正在尝试安装导轨，但出现此错误：
宝石安装导轨 -v 3.2.9
Building native extensions. This could take a while...
ERROR: Error installing rails:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:1:in `<main>'
Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.8.1 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/json-1.8.1/ext/json/ext/generator/gem_make.out
如果我用rails 3.2.9和更多宝石的Gemfile运行bundle install，我会收到此错误：
An error occurred while installing json (1.8.1), and Bundler cannot continue.
Make sure that `gem install json -v '1.8.1'` succeeds before bundling.
你猜怎么着。运行建议的命令会给我另一个错误：
Building native extensions. This could take a while...
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
/usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:1:in `<main>'
Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.8.1 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/json-1.8.1/ext/json/ext/generator/gem_make.out
可能的重复项：
- 无法安装 gem - 无法构建 gem 本机扩展 - 无法加载此类文件 -- mkmf （加载错误） '
- require'：没有要加载的此类文件 -- mkmf （LoadError）
根据您的红宝石版本，运行：
sudo apt-get install ruby1.9.1-dev
一个简单的谷歌搜索指向了这个早期的stackoverflow问题：
为什么我在 Ubuntu 中安装 JSON gem 时出错？
安装 ruby1.9.1-dev 软件包应该可以为您解决此问题：
sudo apt-get install ruby1.9.1-dev