shell commands can't be enabled

snmp4sdn's shell bundle is started and shown as Active, but the shell commands not appear.

opendaylight-user@root>feature:install features-snmp4sdn

opendaylight-user@root> list
300 │ Active │ 80 │ 0.7.0 │ snmp4sdn plugin
301 │ Active │ 80 │ 0.7.0 │ MD-SAL models
302 │ Active │ 80 │ 1.10.0 │ SNMP Java
303 │ Active │ 80 │ 0.7.0 │ snmp4sn plugin shell

opendaylight-user@root>update 303
opendaylight-user@root>log:tail

(then no error or any info appears) 

opendaylight-user@root>printdb

("printdb" is to show snmp4sdn's switch list, but Karaf shell doesn't give this command)