When are all system databases created in an RDBMS?

All system databases in a Relational Database Management System (RDBMS) are created during the RDBMS software installation process. This is when the database environment is set up and all the necessary components—including system databases—are initialized and configured.

The reason this is critical is that system databases often contain essential system structures, metadata, and information necessary for the operation and management of the RDBMS itself. This includes administrative functions like user management, configuration settings, and information about the databases themselves.

The other options relate to various activities within the database management lifecycle but do not encompass the creation of system databases. For instance, data entry focuses on user interactions with the database to input data, while software updates generally modify existing installations without creating new system databases. System reboots are about refreshing the system's state and do not involve creating databases. Therefore, the installation process is the correct time for establishing system databases, setting the foundation for the RDBMS operations.