Running an APM Enterprise Manager (EM) custom install using an existing EM installation directory means that the Installer will go into Upgrade mode because it recognises the presence of the existing installation. This means that:
- An existing installation in directory EM_HOME will be backed up into directory EM_HOME/backup.
- The existing installation will be completely replaced with ONLY the components selected in the new custom install. For example:
- Running a custom install with just WebView selected on an existing installation that has an Enterprise Manager component installed will remove the files relevant to the EM component e.g. files will be removed in directories EM_HOME/config & EM_HOME/product/enterprisemanager
- Running a custom install with Database only selected will cause any EM & WebView components to be lost. This is a task that might be required to upgrade the backup database on a secondary MOM which is sharing the same EM_HOME installation as the primary MOM, so it would also impact the EM_HOME on the primary MOM
In general if running a custom installation it is always best to use a new/separate installation directory to avoid these unintended consequences.