When you have Oracle RAC installed, the crsd process monitors the Oracle database instance, listener, and so on, and automatically restarts these components when a failure occurs. The crsd process generates events when the status of a resource changes. This includes start, stop, monitor, and failover operations. Cluster Ready Services (CRS): The primary program for managing high availability operations in a cluster.The CRS daemon ( crsd) manages cluster resources based on the configuration information that is stored in OCR for each resource.

A cssdagent failure results in Oracle Clusterware restarting the node. This service formerly was provided by Oracle Process Monitor Daemon ( oprocd, also known as OraFenceService on Windows. If you are using certified third-party clusterware, then CSS processes interfaces with your clusterware to manage node membership information.The cssdagent process monitors the cluster and provides I/O fencing.

Oracle Notification Service (ONS): A publish and subscribe service for communicating Fast Application Notification (FAN) events. Event Management (EVM): A background process that publishes events that Oracle Clusterware creates. Cluster Time Synchronization Service (CTSS): Provides time management in a cluster for Oracle Clusterware.

The mDNS process is a background process on Linux and UNIX, and a service on Windows. Multicast Domain Name Service (mDNS): Grid Plug and Play uses the mDNS process to locate profiles in the cluster, as well as by GNS to perform name resolution. Currently has no functionality to be activated in a later release. Grid Interprocess Communication (GIPC): A helper daemon for the communications infrastructure. Grid Plug and Play (GPNPD): GPNPD provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes node have the most recent profile.

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