# update-rc.d apache2 default
update-rc.d: warning: apache2 start runlevel arguments (none) do not match LSB Default-Start values (2 3 4 5)
update-rc.d: warning: apache2 stop runlevel arguments (none) do not match LSB Default-Stop values (0 1 6)
usage: update-rc.d [-n] [-f] <basename> remove
       update-rc.d [-n] <basename> defaults [NN | SS KK]
       update-rc.d [-n] <basename> start|stop NN runlvl [runlvl] [...] .
       update-rc.d [-n] <basename> disable|enable [S|2|3|4|5]
		-n: not really
		-f: force

The disable|enable API is not stable and might change in the future.