How to automatically open all Oracle 12c pluggable databases when starting the container database

First you have to open all pluggable databases and it does not hurt to make the services available…

SQL> alter pluggable database all open services=all;
Pluggable database altered.

Now save the state – next time you start the container – whatever state you saved “all” in (open in this case) will be the state that they are returned to when the container DB is opened

SQL> alter pluggable database all save state;
Pluggable database altered.