Starting with Oracle Database 18c, you can simplify patching and mass rollouts of software across multiple database servers by deploying a read-only Oracle home as a software image.

A read-only Oracle home (ORACLE_HOME) prevents both creation and modification of files inside the Oracle home directory. To configure an Oracle home in read-only mode, you first install Oracle Database software using a software-only deployment, and then configure it as a read-only Oracle home before you create the listener and the database.

Traditional read-write Oracle homes contain instance-specific files, so if you patch them, then you must patch each of them individually. However, when the Oracle home is read-only, instance-specific files are stored separately in the Oracle base directory (ORACLE_BASE), instead of the Oracle home. Because of this configuration, you can use a read-only Oracle home as a software image that you can share across multiple database servers, because it stores only the static files. This option simplifies patching and mass rollout, because when you want to distribute a patch to multiple database servers, you only need to update one Oracle home image.

Apart from the traditional ORACLE_BASE and ORACLE_HOME directories, the following additional directories exist in a read-only Oracle home:

• ORACLE_BASE_HOME: This is a subdirectory within the ORACLE_BASE directory. This directory contains user-specific files, instance-specific files, and log files.

• ORACLE_BASE_CONFIG: This directory is same as the ORACLE_BASE directory. This directory contains instance-specific dynamic files, such as configuration files.