title: rvm --default not setting 1.9.2 ubuntu 11.10 + can't install rails
body: <p>My RVM is 1.9.2</p>
  
  <p>I'm trying to set up rails.  For some reason I can't.  Here's what the env reports:</p>
  
  <pre><code>kevin@V130:~$ rvm list
  
  rvm rubies
  
     ruby-1.8.7-p352 [ x86_64 ]
  =&gt; ruby-1.9.2-p290 [ x86_64 ]
  
  kevin@V130:~$ ruby -v
  ruby 1.8.7 (2011-06-30 patchlevel 352) [x86_64-linux]
  </code></pre>
  
  <p>Shouldn't that be listing 1.9.2?  It's been set as the --default.</p>
  
  <p>when I gem <code>install rails</code> I get </p>
  
  <pre><code>kevin@V130:~$ sudo gem install rails
  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
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require': no such file to load -- mkmf (LoadError)
      from &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
      from extconf.rb:1:in `&lt;main&gt;'
  
  
  Gem files will remain installed in /var/lib/gems/1.9.1/gems/json-1.6.3 for inspection.
  Results logged to /var/lib/gems/1.9.1/gems/json-1.6.3/ext/json/ext/parser/gem_make.out
  kevin@V130:~$ 
  </code></pre>