Me too. Took ages to hit the “duh” moment, then it became pretty obvious! The file
/etc/init.d/oracle also known as
rcoracle to root users can be used to do a number of things such as starting the databases, starting the (default LISTENER) listener, CRS etc but, as I eventually found out, you have to configure it to do so!
The configuration file is
Most of the options are defaulted to off, except for the setting of kernel parameters (
SET_ORACLE_KERNEL_PARAMETERS="yes") which is very useful.