# gem install json -v '1.8.2'
Building native extensions. This could take a while…
ERROR: Error installing json:
ERROR: Failed to build gem native extension.
/usr/bin/ruby extconf.rb
mkmf.rb can’t find header files for ruby at /usr/share/include/ruby.h
Gem files will remain installed in /usr/local/share/gems/gems/json-1.8.2 for inspection.
Results logged to /usr/local/share/gems/gems/json-1.8.2/ext/json/ext/generator/gem_make.out
解决上述问题，需要安装如下包。
# yum install ruby-devel