Search notes:

RMAN command: configure

backup archivelog all;
backup database;
backup database plus archivelog;
backup incremental;
backup spfile;

Channel

configure channel has the same options as allocate.

Return a configuration value to its default value:

configure backup optimization clear;
configure retention policy clear;
configure controlfile autobackup format for device type disk clear;

configure default device type to SBT;
configure default device type to disk;

A configured default device type can be overwritten in a backup command with backup DEVICE TYPE SBT database.