For context, it on a remote server which has a firewall. I'm setting up my environment through a proxy. I have ruby 1.8.7. When I try to gem install.. sudo gem install --http-proxy <host address>:<port> json I get the following error: 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 ca
![Error while installing json gem 'mkmf.rb can't find header files for ruby'](https://cdn-ak-scissors.b.st-hatena.com/image/square/98d6f053a97a87156775f60757c60865d0f2c47d/height=288;version=1;width=512/https%3A%2F%2Fcdn.sstatic.net%2FSites%2Fstackoverflow%2FImg%2Fapple-touch-icon%402.png%3Fv%3D73d79a89bded)