Saads-Mac-Pro:~ SMD$ gem install rails
Building native extensions.  This could take a while...
/Users/SMD/.rvm/rubies/ruby-2.0.0- p247/lib/ruby/site_ruby/2.0.0/rubygems/ext/builder.rb:54: warning: Insecure world writable dir /usr in PATH, mode 040777
ERROR:  Error installing rails:
ERROR: Failed to build gem native extension.

/Users/SMD/.rvm/rubies/ruby-2.0.0-p247/bin/ruby extconf.rb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/Users/SMD/.rvm/rubies/ruby-2.0.0-p247/bin/ruby
--with-atomic_reference-dir
--without-atomic_reference-dir
--with-atomic_reference-include
--without-atomic_reference-include=${atomic_reference-dir}/include
--with-atomic_reference-lib
--without-atomic_reference-lib=${atomic_reference-dir}/
/Users/SMD/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/mkmf.rb:434:in `try_do': The  compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /Users/SMD/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/mkmf.rb:519:in `try_link0'
from /Users/SMD/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/mkmf.rb:817:in `try_run'
from extconf.rb:24:in `<main>'


Gem files will remain installed in /Users/SMD/.rvm/gems/ruby-2.0.0-p247/gems/atomic-1.1.13 for inspection.
Results logged to /Users/SMD/.rvm/gems/ruby-2.0.0-p247/gems/atomic-1.1.13/ext/gem_make.out

Это вывод, когда я запускаю эту командуgem install rails, Что я делаю неправильно? Заранее спасибо

РЕДАКТИРОВАТЬ:

Выход изgem env:

Saads-Mac-Pro:~ SMD$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 2.0.7
  - RUBY VERSION: 2.0.0 (2013-06-27 patchlevel 247) [x86_64-darwin12.3.0]
  - INSTALLATION DIRECTORY: /Users/SMD/.rvm/gems/ruby-2.0.0-p247
  - RUBY EXECUTABLE: /Users/SMD/.rvm/rubies/ruby-2.0.0-p247/bin/ruby
  - EXECUTABLE DIRECTORY: /Users/SMD/.rvm/gems/ruby-2.0.0-p247/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-darwin-12
  - GEM PATHS:
     - /Users/SMD/.rvm/gems/ruby-2.0.0-p247
     - /Users/SMD/.rvm/gems/ruby-2.0.0-p247@global
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/