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The ONS Daemon Explained In Oracle Clusterware/RAC Environment (Doc ID 759895.1)

Last updated on APRIL 30, 2023

Applies to:

Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Database - Enterprise Edition - Version and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.


This note is intended to explain the purpose of the ONS daemon, how it is configured and what need to be checked when troubleshooting a ONS related problem in an Oracle Clusterware installation.


DBA and Oracle Clusterware installers


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In this Document
 1. purpose of the ons daemon
 2. launching the ons daemon
 3. configuration of the ons daemon prior to 11gR2
 4. configuration of the ons daemon in 11gR2
 4.1 Setting the localport and remoteport via srvctl in 11gR2
 4.2 to set the debug level ( see onsctli usage for a detailed descrition) in 11gR2
 5. ons clients/subscribers
 5.1 the listeners are subscribers for the ons daemon
 5.2 application clients/subscribers
 6. the FAN and RLB events
 6.1 the FAN events
 6.1.1 FAN events forwarded to the ons daemon by 11gR2 agent or pre-11gR2 racgimon
 6.1.2 FAN events forwarded from the evmd daemon to the ons daemon
 6.2 the RLB events

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