ruby - Failed to build gem native extension — Rails install

Question

I have been installing Ruby on Rails based on the instruction from edX online class.

Here is a list of terminal commands, and, where relevant, corresponding output:

$ sudo apt-get install ruby1.9.1

installation successful

$ wget http://production.cf.rubygems.org/rubygems/rubygems-1.8.24.tgz
$ tar zxvf ruby-1.8.24.tgz
$ cd ruby-1..8.24
$ sudo ruby setup.rb
RubyGems 1.8.24 installed

== 1.8.24 / 2012-04-27

* 1 bug fix:

  * Install the .pem files properly. Fixes #320
  * Remove OpenSSL dependency from the http code path


------------------------------------------------------------------------------

RubyGems installed the following executables:
    /usr/bin/gem1.9.1

Up to here, everything looked fine, but the I tried to install rails and failed:

$ sudo gem install rails
Fetching: i18n-0.6.1.gem (100%)
Fetching: multi_json-1.3.6.gem (100%)
Fetching: activesupport-3.2.8.gem (100%)
Fetching: builder-3.0.3.gem (100%)
Fetching: activemodel-3.2.8.gem (100%)
Fetching: rack-1.4.1.gem (100%)
Fetching: rack-cache-1.2.gem (100%)
Fetching: rack-test-0.6.1.gem (100%)
Fetching: journey-1.0.4.gem (100%)
Fetching: hike-1.2.1.gem (100%)
Fetching: tilt-1.3.3.gem (100%)
Fetching: sprockets-2.1.3.gem (100%)
Fetching: erubis-2.7.0.gem (100%)
Fetching: actionpack-3.2.8.gem (100%)
Fetching: arel-3.0.2.gem (100%)
Fetching: tzinfo-0.3.33.gem (100%)
Fetching: activerecord-3.2.8.gem (100%)
Fetching: activeresource-3.2.8.gem (100%)
Fetching: mime-types-1.19.gem (100%)
Fetching: polyglot-0.3.3.gem (100%)
Fetching: treetop-1.4.10.gem (100%)
Fetching: mail-2.4.4.gem (100%)
Fetching: actionmailer-3.2.8.gem (100%)
Fetching: rake-0.9.2.2.gem (100%)
Fetching: rack-ssl-1.3.2.gem (100%)
Fetching: thor-0.16.0.gem (100%)
Fetching: json-1.7.5.gem (100%)
Building native extensions.  This could take a while...
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/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
    from /usr/local/lib/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from extconf.rb:1:in `<main>'


Gem files will remain installed in /usr/lib/ruby/gems/1.9.1/gems/json-1.7.5 for inspection.
Results logged to /usr/lib/ruby/gems/1.9.1/gems/json-1.7.5/ext/json/ext/generator/gem_make.out

Answer 1

mkmf is part of the ruby1.9.1-dev package. This package contains the header files needed for extension libraries for Ruby 1.9.1. You need to install the ruby1.9.1-dev package by doing:

sudo apt-get install ruby1.9.1-dev

Then you can install Rails as per normal.

Generally it's easier to just do:

sudo apt-get install ruby-dev