In any execution of the migration utility, before the utility migrates your customizations from the backup directory to your new installation, it creates a backup of certain files in your current new local and stores it in a .rollback_<version_timestamp> directory. Also, it records the version and timestamp before any migration.
The rollback option allows you to reverse the changes made by the migration utility by restoring the local version in your new installations using files from the .rollback_<version_timestamp> directory. Rollback will contain only those locals which are part of migration.
In some scenarios, if a file is copied to the new installation with .<old_version> extension, then this file is not deleted when a rollback is performed.
The rollback action is restricted only to rollback points that were recorded in your current version. For example if you upgrade from 126.96.36.199 to 188.8.131.52, and then install a patch (for example, 184.108.40.206), the rollback utility will not allow you to rollback to your 220.127.116.11 local version. You have to manually uninstall the patch in order to rollback to 18.104.22.168.
You can use the rollback option only after an in-place upgrade or if you have previously run the migration utility either in the SAME_HOST, DIFFERENT_HOST or UPGRADE_NEW modes.
Perform a rollback on page 90 describes the procedure for carrying out a rollback.