RAC Oracle Clusterware Startup Sequence 12c

12c Oracle Clusterware Startup Sequence - Oracle clusterware startup automatically when the RAC node starts. Startup sequence process tuns through different levels, in below figure you can find how multiple level startup process to start the full grid infrastructure stack also how the resources that clusterware manage.

This tutorial will describe startup sequence of oracle 12c RAC clusterware which is installed on Unix / Linux platform.

Oracle 12c RAC Clusterware Startup Sequence

Once your Operating system finish the boot scrap pocess it reads /etc/init.d file via the initialisation daemon names init or init.d. In the init tab file is the one it triggers oracle high availability service daemon.

$cat /etc/inittab | grep init.d | grep -v grep
h1:35:respawn:/etc/init.d/init.ohasd run  >/dev/null  2>&1 </dev/null
Oracle Linux 6.x and Red Hat Linux 6.x have deprecated inittab.  init.ohasd is configured in startup in /etc/init/oracle-ohasd.conf:

$cat /etc/init/oracle-ohasd.conf

 start on runLevel [35]
start on tunLevel [!35]
respawn
exec /etc/init.d/init.ohasd run > /dev/null  2>&1 <dev/null
this start up " init.ohasd run " , which in turn starts up the ohasd.bin background process :

$ps  -ef  | grep  ohasd  | grep  -v grep
root  4056  1  1  Feb19   ?     01:54:34 /u01/app/12.1.0/grid/bin/ohsd.bin  reboot
root  2715  1   0 Feb19  ?     00:00:00  /bin/sh   /etc/init.d/init.ohsd  run

OHASD ( Oracle High Availability Service Daemon )  - we also call it as oracle restart

First /etc/init triggers OHASD, once ohasd is started on Level 0, it is responsible for starting the rest of clusterware and the resources that clusterware manages directly or indirectly through Levels 1- 4.

Level 1 - Ohasd on it own triggers four agent process

• cssdmonitor : CSS Monitor
• OHASD orarootagent : High Availability Service stack Oracle root agent
• OHASD oraagent : High Availability Service stack Oracle Agent
• cssdagent : CSS Agent

Level 2 - On this level, OHASD ora agent trigger five processes

• mDNSD : mDNS daemon process
• GIPCD : Grid Interprocess Comunication
• GPnPD : GPnP Profile daemon
• EVMD : Even Monitor Daemon
• ASM : Resources for monitoring ASM Instances

Then, OHASD oraclerootagent trigger following processes 

• CRSD : CRS daemon
• CTSSD : Cluster Time Synchronisation Service Daemon 
• Diskmon : Disk Monitor Daemon ( Exadata Server Storage )
• ACFS : ( ASM Cluster File System ) Drivers

Next, the cssdagent starts the CSSD ( CSS daemon ) process.

Level 3 - The CRSD spawns two CRSD agents : CRSD orarootagent and CRSD oracleagent.

Level 4 - On this levael, the CRSD orarootagent is responsible for starting he following resources :

• Network resource : for the public network
• SCAN VIPs
• Node VIPs : VIPs for each node
• ACFS Registry
• GNS VIP : VIP for GNS if you use the GNS option

Then, the CRSD orarootagent is responsible for starting the rest of the resources as follow 

• ASM Resources : ASM instances(s) resource
• Diskgroup : Used for managing / monitoring ASM diskgroups
• Disk Resource : Used for managing and monitoring the DB and instances
• SCAN Listener : Listener for SCAN listening on SCAN VIP
• Listener : Node Listener listening on the Node VIP
• Services : Database Services
• ONS
• eONS : Enhanced ONS
• GSD : For 9i backword compatibility
• GNS : performs name resolution ( Optional )