see these posts.. it seems that piping "tail -f" works with some OSes and does not work with some...

http://www.computing.net/solaris/www...orum/1734.html

http://www.zsh.org/mla/users/1999/msg00360.html

you did not tell whether...

tail -f log_X | grep n

worked on your system.. i.e., you can see the stuff on your terminal..

Cheers!
Vishnu.