使用Ubuntu，当我运行“ bundle install ”来设置我的Rails环境时，在JSON gem安装过程中会引发一个错误：
Installing json (1.7.3) with native extensions Gem::Installer::ExtensionBuildError: 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 /home/danny/.bundler/tmp/2040/gems/json-1.7.3 for inspection. Results logged to /home/danny/.bundler/tmp/2040/gems/json-1.7.3/ext/json/ext/parser/gem_make.out An error occured while installing json (1.7.3), and Bundler cannot continue. Make sure that `gem install json -v '1.7.3'` succeeds before bundling.
当我尝试只安装JSON 1.7.3的gem时，也给我一个错误：
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-1.7.3 for inspection. Results logged to /var/lib/gems/1.9.1/gems/json-1.7.3/ext/json/ext/parser/gem_make.out
我已经安装了RVM，并运行Ruby 1.9.3; 为什么不能安装JSON gem？
安装ruby1.9.1-dev包应该为你解决这个问题：
sudo apt-get install ruby1.9.1-dev