gem install json失败_gem install json -v '2.6.3

# gem install json -v '1.8.3'
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 `<main>'
 
 
Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.8.3 for inspection.
Results logged to /var/lib/gems/1.9.1/gems/json-1.8.3/ext/json/ext/generator/gem_make.out

# sudo apt-get install ruby-dev

or 

yum install ruby-devel