$ gem install rails

Building native extensions.  This could take a while...
    ERROR:  Error installing rails:
    ERROR: Failed to build gem native extension.

    /usr/bin/ruby -r ./siteconf20150707-4993-mpal0w.rb extconf.rb
    mkmf.rb can't find header files for ruby at /usr/lib/ruby/include /ruby.h

    extconf failed, exit code 1

Gem files will remain installed in /usr/lib/ruby/gems/2.2.0/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /usr/lib/ruby/gems/2.2.0/extensions/armle-linux/2.2.0/nokogiri-1.6.6.2/gem_make.out

curl: (23) Failed writing body (0 != 15755)