rgrep search on emacs
 

Hi, everyone!
I am using emacs24 on crunchbang and using very often the emacs command "M-x rgrep." What annoys me is that everytimes when it starts to search it always prompts to ask for inputting the directory-name and file-type, I would like to reset it to search in a personally defined default directory and use "all" for file-type. Does anyone know how to modify the function of the command "rgrep?"
best wishes
Sumatibhadra