作为上下文，它位于具有防火墙的远程服务器上。我正在通过代理设置环境。我有ruby 1.8.7。当我尝试gem安装..

sudo gem install --http-proxy <host address>:<port> json

我得到以下错误:

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/lib/ruby/ruby.h

Gem files will remain installed in /usr/lib64/ruby/gems/1.8/gems/json-1.8.1 for inspection.
Results logged to /usr/lib64/ruby/gems/1.8/gems/json-1.8.1/ext/json/ext/generator/gem_make.out

因为我不确定是什么问题，我谷歌了一下，找到了这些

gem安装:构建gem本地扩展失败(找不到头文件)-这里的说明似乎是特定于正在安装的gem。 如何安装json gem -未能建立gem本地扩展这似乎是略有不同的错误。

有提示吗?谢谢!