CRS-4535: Cannot communicate with Cluster Ready Services

If checking status of CRS (and other RAC resources) returns you this error, it means that CRS is not running.

[grid@dbnode1 ]$ crsctl stat res -t CRS-4535: Cannot communicate with Cluster Ready Services CRS-4000: Command Status failed, or completed with errors.

OEM Database Control Configuration gets Stuck

I encountered a situation where I was trying to configure OEM Database Control (11.2.0.4) on Windows based system using command similar to the following

emca -config dbcontrol db -repos recreate

ORA-00221: error on write to controlfile

Reason of this error (and probably instance crash) is that some other process has locked the controlfile and oracle process is not able to get hold of a lock on the controlfile before it could write in it. Most probable reason for this is some third party backup solution that might be copying oracle related files in backup process and hence holding a lock while copying.