为什么我的rubgems没有与二进制文件建立符号链接？

I'm on Ubuntu 11.04 with ruby 1.9.2p180 installed from source using rvm. When I install a gem that makes a command-line binary, links are not made. For example, when I install the passenger gem, I'm on Ubuntu 11.04 with ruby 1.9.2p180 install