gem 安装 json 报错

问题

编译一个开源书辑时，运行 bundle install 命令报错，让安装 json -v ‘1.8.1’，但报错。

sudo gem install json -v '1.8.1'

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 `&lt;main&gt;'

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

`</pre>

## 解决

添加 ruby1.9.1-dev包就可以解决这个问题了。

<pre>`sudo apt-get install ruby1.9.1-