li44-63:~# gem install passenger
Install required dependency fastthread? [Yn]  y
Select which gem to install for your platform (i486-linux)
 1. fastthread 1.0.1 (mswin32)
 2. fastthread 1.0.1 (ruby)
 3. fastthread 1.0.1 (i386-mswin32)
 4. Cancel installation
> 2
Building native extensions.  This could take a while...
extconf.rb:1:in `require': no such file to load -- mkmf (LoadError)
        from extconf.rb:1

ERROR:  While executing gem ... (RuntimeError)
    ERROR: Failed to build gem native extension.
Gem files will remain installed in /var/lib/gems/1.8/gems/fastthread-1.0.1 for inspection.


Results logged to /var/lib/gems/1.8/gems/fastthread-1.0.1/ext/fastthread/gem_make.out
li44-63:~# gem install passenger
Install required dependency fastthread? [Yn]  n
ERROR:  While executing gem ... (Gem::DependencyError)
    Required dependency fastthread not installed