Modifying /etc/defaults/snmpd and setting "-Lsd" to "-LS6d" in SNMPDOPTS and TRAPDOPTS hides the error message (as suggested by
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=559109).
Or you can use `sed -i "s|-Lsd|-LS6d|" /etc/default/snmpd` to fix the problem.