While upgrading Grid Infrastructure (GI) from 12.1.0.2 to 12.2.0.1, gridSetup.sh reports missing pre-requisite patch 21255373 even though patch is already available
$ /u01/app/12.1.0/grid/OPatch/opatch lsinventory|grep 21255373
22393909, 21255373, 25164540, 18868829, 20408163, 20579351, 20350915
It is a bug. the workaround is to use ‘gridSetup.sh -skipPrereqs’ after verifying all other pre-requisites successfully.
$ /u01/app/12.2.0.1/grid/gridSetup.sh -skipPrereqs