Trouble installing passenger gem on Ubuntu

From the console:

 adelevie@ubuntu:~$ gem install passenger
    Building native extensions.  This could take a while...
    ER开发者_开发问答ROR:  Error installing passenger:
        ERROR: Failed to build gem native extension.

    /usr/bin/ruby1.8 extconf.rb
    /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require': no such file to load -- mkmf (LoadError)
        from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `require'
        from extconf.rb:8


    Gem files will remain installed in /home/adelevie/ruby/gems/gems/fastthread-1.0.7 for inspection.
    Results logged to /home/adelevie/ruby/gems/gems/fastthread-1.0.7/ext/fastthread/gem_make.out

What does this mean and what are my options?

---

it's actually

apt-get install ruby1.8-dev

doing this fixed the problem building passenger for me

---

You need to install the ruby-dev pacakge.

apt-get install ruby-dev1.8