why i can use CELL to be my output device

[ng at rti-md.com]

Well you need to enable that in the monitor cap file in the
$(GISBASE)/etc/monitorcap file. You can do that by inserting
the following:

CELL:driver/CELL:Create GRASS Raster File: \
     /home/grass4.1/dev/fifo.8a /home/grass4.1/dev/fifo.8b \
     ::any terminal

Hope this helps 

Nalneesh Gaur