Why does `gem install rails` fail?

Question

As a background, here's my environment:

vishal@dishDell:~$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.8.24
  - RUBY VERSION: 1.9.3 (2011-10-30 patchlevel 0) [x86_64-linux]
  - INSTALLATION DIRECTORY: /usr/lib/ruby/gems/1.9.1
  - RUBY EXECUTABLE: /usr/bin/ruby1.9.1
  - EXECUTABLE DIRECTORY: /usr/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /usr/lib/ruby/gems/1.9.1
     - /home/vishal/.gem/ruby/1.9.1
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

This is what happens when I try running gem install rails.

vishal@dishDell:~$ sudo gem install rails
[sudo] password for vishal: 
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-1.7.3 for inspection.
Results logged to /usr/lib/ruby/gems/1.9.1/gems/json-1.7.3/ext/json/ext/parser/gem_make.out

I installed Ruby 1.9.3 using apt-get, and I installed RubyGems from a tarball at rubygems.org. What should I do to get this to work?

Answer 1

this worked for me with Ubuntu 12.10:

sudo apt-get install ruby
sudo apt-get install ruby-dev
sudo apt-get install rubygems
sudo gem install rails

Answer 2

As pointed out in this other Stackoverflow question, check if you have ruby-1.9-dev or ruby-1.9.3-dev package. Install it if missing and then try install rails.

Also, have a look at RVM to install and manage multiple ruby versions at the same time.