Use this procedure to downgrade Oracle Standalone Cluster after a successful upgrade.

1. As the grid user, downgrade the GIMR using the command syntax mgmtua downgrade gimrHome from 21c GIMR home directory after a successful upgrade:

   $ $ORACLE_HOME/bin/mgmtua downgrade gimrHome

   Note:

   Run this step only if the GIMR is configured locally and upgrade is failed after Oracle Grid Infrastructure is upgraded successfully. The GIMR home is not required after the downgrade is complete.
2. As the root user, use the command syntax rootcrs.sh -downgrade from 21c Grid home to downgrade Oracle Grid Infrastructure on all nodes, in any sequence. For example:

   # $ORACLE_HOME/crs/install/rootcrs.sh -downgrade

   Run this command from a directory that has write permissions for the Oracle Grid Infrastructure installation user. You can run the downgrade script in parallel on all cluster nodes, but one.

3. Downgrade the last node after you downgrade all other nodes:

   # $ORACLE_HOME/crs/install/rootcrs.sh -downgrade

4. As the grid user, remove Oracle Grid Infrastructure 21c Grid home as the active Oracle Clusterware home:

   1. On any of the cluster member nodes where the rootupgrade.sh script has run successfully, log in as the Oracle Grid Infrastructure installation owner.

   2. Use the following command to start the installer, where /u01/app/21.0.0/grid is the location of the new (upgraded) Grid home:

      $ cd $ORACLE_HOME/oui/bin 
      $ ./runInstaller -nowait -waitforcompletion -ignoreSysPrereqs -updateNodeList -silent CRS=false 
      ORACLE_HOME=/u01/app/21.0.0/grid "CLUSTER_NODES=node1,node2,node3" -doNotUpdateNodeList 

      Add the flag -cfs if the Grid home is a shared home.

5. Set previous release Grid home as the active Oracle Clusterware home:

   1. On any of the cluster member nodes where the rootupgrade script has run successfully, log in as the Oracle Grid Infrastructure installation owner.

   2. Use the following command to start the installer, where the path you provide for ORACLE_HOME is the location of the home directory from the earlier Oracle Clusterware installation.

      $ cd $ORACLE_HOME/oui/bin 
      $ ./runInstaller -nowait -waitforcompletion -ignoreSysPrereqs 
      -updateNodeList -silent CRS=true 
      ORACLE_HOME=pre-upgrade-grid-home
      "CLUSTER_NODES=node1,node2,node3"

   pre-upgrade-grid-home is the previous release Grid home.

6. As the root user, start the Oracle Clusterware stack on all nodes from previous release Grid home.

   # crsctl start crs

7. As  the grid user, run the GIMR_recreate.sh script from 21c Oracle Base directory to recreate the GIMR container:

   $ $ORACLE_BASE/admin/mgmtdb/GIMR_recreate.sh

   Note:

   Run this step only if the GIMR is configured locally in the cluster and upgrade is failed after rootupgade.sh is run successfully on all of the cluster nodes.