To start with nepenthes as sensor for prelude, you have to create a
starting profile, e.g. "nepenthes" by running on the manager side:
 
# prelude-adduser registration-server prelude-manager \
        --uid=564 --gid=564
 
and on the sensor side:
 
# prelude-adduser register nepenthes "idmef:w" \
        <manager address> --uid 564 --gid 564
 
Then, enable prelude logging in ${SYSCONFDIR}/nepenthes/nepenthes.conf
(uncomment the "logprelude.so" line).

Eventually, fill in ${SYSCONFDIR}/nepenthes/log-prelude.conf if needed,
before starting nepenthes.