No command 'bleak' found

[sunnyting]

I installed bleak_house as gem and it appears installed successfully.
I can found the message "* Bleakhouse: installed" when my server stared and messages "
* BleakHouse: working...
* BleakHouse: complete
* Bleakhouse: Run 'bleak /tmp/bleak._.dump' to analyze." when my server stopped.
But when I try to run "bleak /tmp/bleak._*.dump" on my terminal, I got the error:
"
No command 'bleak' found, did you mean:
Command 'mleak' from package 'mpatrolc2' (universe)
bleak: command not found
"

And I searched a lot but seems no other people had the same issue as mine.
My OS is ubuntu 9.04 and the result of "ruby -v" is "ruby 1.8.7".
Any thought about it?
Thanks in advance.