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?
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.