Rprofile.site can't work
===

my system :debian
in console:
nano   /home/tiger/R-2.15.1/etc/Rprofile.site   
here is my content:

    .First <- function(){    
         cat("\nWelcome at", date(), "\n")
         }

    .Last <- function(){
        cat("\nGoodbye at ", date(), "\n")
        }

when i save it ,reopen my  R ,
why there is no  
Welcome at Sun Jul 15 07:53:58 2012
in my  R?