Line 327 of the karaf-service script in the karaf/shell subproject uses the su command with flags that are unsupported under Solaris 11:

su -m $RUN_AS_USER -s /bin/sh -c "$REALPATH $1"

Options -m and -s are not recognized under Solaris. Maybe replace with something like:

su - $RUN_AS_USER -c "$REALPATH $1"