Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

Specific Errors and Solutions
1

Operating System:
Debian 7.1
Description:
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

Gem::Installer::ExtensionBuildError: 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>'

Solution:
Missing ruby development package. Install a relevant ruby-dev package. For example

# apt-get install ruby1.9.1-dev