You are installing Oracle Database 11g on your server. During the installation Oracle Universal Installer (OUI) prompts you to enter the path of the inventory directory and also prompts you to…

ORACLE_BASE not being set affects the default suggested path for the Oracle home, but OUI prompting for inventory directory and OS group is specifically triggered by the absence of a pre-existing central inventory (first install), not by ORACLE_BASE being unset.

Oracle strongly discourages installing as root and OUI will actually warn or block a root-user installation; the inventory prompt appears for any valid Oracle OS user performing a first-time install, not exclusively for root.

The OS group specified for inventory ownership (oinstall) does not need root as a member; it simply needs write access to the oraInventory directory, and root membership is neither required nor recommended.

The 'Create Starter Database' option controls whether a default database (ORCL) is created post-installation and is entirely unrelated to why OUI prompts for the inventory directory and OS group name.

The first time Oracle software is installed on a host, OUI needs to create the central inventory directory (oraInventory) and must know which OS group (typically 'oinstall') will own and manage it. That OS group must be granted write permissions to the inventory directory so that OUI and future Oracle installations can register installed products, update inventory metadata, and run scripts like orainstRoot.sh. Without write access for the group, the installation cannot complete successfully.