oracle database 12c silent installation

if you are used to use silent installation for the oracle database software you need to provide additional parameters: oracle.install.db.BACKUPDBA_GROUP, oracle.install.db.DGDBA_GROUP and oracle.install.db.KMDBA_GROUP

./runInstaller oracle.install.option=INSTALL_DB_SWONLY \
    ORACLE_BASE=/opt/oracle/product/base \
    ORACLE_HOME=/opt/oracle/product/base/12.1.0.1 \
    UNIX_GROUP_NAME=oinstall \
    oracle.install.db.DBA_GROUP=dba \
    oracle.install.db.OPER_GROUP=oper \
    oracle.install.db.BACKUPDBA_GROUP=dba \
    oracle.install.db.DGDBA_GROUP=dba \
    oracle.install.db.KMDBA_GROUP=dba \
    FROM_LOCATION=../stage/products.xml \
    INVENTORY_LOCATION=/opt/oracle/oraIventory \
    SELECTED_LANGUAGES=en \
    oracle.install.db.InstallEdition=EE \
    DECLINE_SECURITY_UPDATES=true  -silent -ignoreSysPrereqs -ignorePrereq -waitForCompletion

otherwise your installation will fail with:

[FATAL] [INS-35341] The installation user is not a member of the following groups: [null, null, null]
   CAUSE: The installation user account must be a member of all groups required for installation.
   ACTION: Ensure that the installation user is a member of the system privileges operating system groups you selected.

these are used to further improve seperation of duties: documentation