Use this procedure to downgrade to Oracle Grid Infrastructure 12c Release 1 (12.1).

1. Delete the Oracle Grid Infrastructure 19c Management Database:

   $ dbca -silent -deleteDatabase -sourceDB -MGMTDB 

2. Use the command syntax rootcrs.sh -downgrade to downgrade Oracle Grid Infrastructure on all nodes, in any sequence. For example:

   # /u01/app/19.0.0/grid/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:

   # /u01/app/19.0.0/grid/crs/install/rootcrs.sh -downgrade

4. Remove Oracle Grid Infrastructure 19c 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/19.0.0/grid is the location of the new (upgraded) Grid home:

      $ cd /u01/app/19.0.0/grid/oui/bin
      ./runInstaller -nowait -waitforcompletion -ignoreSysPrereqs
      -updateNodeList -silent CRS=false 
      ORACLE_HOME=/u01/app/19.0.0/grid
      "CLUSTER_NODES=node1,node2,node3" 
       -doNotUpdateNodeList 

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

5. Set Oracle Grid Infrastructure 12c Release 1 (12.1) 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 /u01/app/12.1.0/grid/oui/bin 
      $ ./runInstaller -nowait -waitforcompletion -ignoreSysPrereqs 
      -updateNodeList -silent CRS=true 
      ORACLE_HOME=/u01/app/12.1.0/grid
      "CLUSTER_NODES=node1,node2,node3"

6. Start the 12.1 Oracle Clusterware stack on all nodes.

   # crsctl start crs

7. On any node, remove the MGMTDB resource as follows:

   $ 121_Grid_home/bin/srvctl remove mgmtdb

8. If you are downgrading to Oracle Grid Infrastructure 12c Release 1 (12.1.0.2), run the following commands to configure the Grid Infrastructure Management Database:

   1. Run DBCA in the silent mode from the 12.1.0.2 Oracle home and create the Management Database container database (CDB) as follows:

      12102_Grid_home/bin/dbca -silent -createDatabase -createAsContainerDatabase true 
      -templateName MGMTSeed_Database.dbc -sid -MGMTDB -gdbName _mgmtdb 
      -storageType ASM -diskGroupName ASM_DG_NAME
      -datafileJarLocation 12102_Grid_home/assistants/dbca/templates
      -characterset AL32UTF8 -autoGeneratePasswords -skipUserTemplateCheck

   2. Run DBCA in the silent mode from the 12.1.0.2 Oracle home and create the Management Database pluggable database (PDB) as follows:

      12102_Grid_home/bin/dbca -silent -createPluggableDatabase -sourceDB
       -MGMTDB -pdbName cluster_name -createPDBFrom RMANBACKUP 
      -PDBBackUpfile  12102_Grid_home/assistants/dbca/templates/mgmtseed_pdb.dfb 
      -PDBMetadataFile  12102_Grid_home/assistants/dbca/templates/mgmtseed_pdb.xml 
      -createAsClone true -internalSkipGIHomeCheck

9. If you are downgrading to Oracle Grid Infrastructure 12c Release 1 (12.1.0.1), run DBCA in the silent mode from the 12.1.0.1 Oracle home and create the Management Database as follows:

   12101_Grid_home/bin/dbca -silent -createDatabase 
   -templateName MGMTSeed_Database.dbc -sid -MGMTDB -gdbName _mgmtdb 
   -storageType ASM -diskGroupName ASM_DG_NAME
   -datafileJarLocation 12101_Grid_home/assistants/dbca/templates
   -characterset AL32UTF8 -autoGeneratePasswords

10. Configure the Management Database by running the Configuration Assistant from the location 121_Grid_home/bin/mgmtca.