[Rails] Rails Instillation Error

I installed the ruby 1.9.3. while instillation rails, I am getting
instillation error. Below is the error

ERROR: Error installing rails:
ERROR: Failed to build gem native extension.

/usr/bin/ruby1.9.1 extconf.rb
/usr/local/lib/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:45:in
`require': cannot load such file -- mkmf (LoadError)
from
/usr/local/lib/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:45:in
`require'
from extconf.rb:1:in `<main>'


Gem files will remain installed in
/usr/lib/ruby/gems/1.9.1/gems/json-1.8.0 for inspection.
Results logged to
/usr/lib/ruby/gems/1.9.1/gems/json-1.8.0/ext/json/ext/generator/gem_make.out

Please anyone help me out

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