Start up sequence:

The operating system starts ohasd (how):

Once the Operating system starts and finish the boot scrap process it reads /etc/init.d file via the initialisation daemon (INIT daemon >>) called init or init.d. The init tab file is the one it triggers oracle high availability service daemon

INIT daemon is very first daemon to be start  at the time of the operating system boot, we can say it  is system and service manager for the oracle linuxor any linux flavor. This services are start and stop through script which is stored in the /etc/init.d directory .

OHASD:-

Oracle High Availability Daemon   is the introduced in oracle 11g which is manage all clusterware resources , it is  responsible to start and monitor all local oracle clusterware daemon. We can say it is anchor for the all the process .

cat /etc/inittab|grep init.ohasd

h1:35:respawn:/etc/init.d/init.ohasd run >/dev/null 2>&1 </dev/null

HAS startup sequence:

– /etc/inittab

– /etc/init.d/init.ohasd

– /etc/rc.d/init.d/ohasd

– $GRID_HOME/bin/ohasd.bin

“/etc/init.d/init.ohasd” is started at runlevel 3 (networked, multi-user mode) or runlevel 5 (runlevel 3 + GUI).Logs present under “$GRID_HOME/log/<host_name>“.

/etc/inittab >>/etc/init.d/init.ohasd>>>/etc/rc.d>init.d/ohasd>>$GRID_HOME/ohasd.bin

“crsctl disable crs” updates a flag in “/etc/orale/scls_scr/<host_name>/root/ohasdstr“.

This file either contains “enable” or “disable” without any carriage return.

If “disable“, “/etc/rc.d/init.d/ohasd” will not startup.

nohup /etc/init.d/init.ohasd run &

 ohasd starts agents(whic all agent):

cssdagent - Agent responsible for spawning CSSD. >>> CSSD 

orarootagent - Agent responsible for managing all root owned ohasd resources.

         CRSD - Primary daemon responsible for managing cluster resources.

         CTSSD - Cluster Time Synchronization Services Daemon

         Diskmon

         ACFS (ASM Cluster File System) Drivers

oraagent - Agent responsible for managing all oracle owned ohasd resources.

         MDNSD - Used for DNS lookup

         GIPCD - Used for inter-process and inter-node communication

         GPNPD - Grid Plug & Play Profile Daemon

         EVMD - Event Monitor Daemon

         ASM - Resource for monitoring ASM instances  

cssdmonitor - Monitors CSSD and node health (along wth the cssdagent).

         CSSDmonitor

to start up daemons (gipcd, mdnsd, gpnpd, ctssd, ocssd,crsd, evmd asm etc), and 

crsd starts agents Which)

orarootagent - Agent responsible for managing all root owned crsd resources.

            Network resource - To monitor the public network

            SCAN VIP(s) - Single Client Access Name Virtual IPs

            Node VIPs - One per node

            ACFS Registery - For mounting ASM Cluster File System

            GNS VIP (optional) - VIP for GNS

oraagent - Agent responsible for managing all oracle owned crsd resources.

           ASM Resouce - ASM Instance(s) resource

           Diskgroup - Used for managing/monitoring ASM diskgroups.

           DB Resource - Used for monitoring and managing the DB and instances

           SCAN Listener - Listener for single client access name, listening on SCAN VIP

           Listener - Node listener listening on the Node VIP

           Services - Used for monitoring and managing services

           ONS - Oracle Notification Service

           eONS - Enhanced Oracle Notification Service

           GSD - For 9i backward compatibility

           GNS (optional) - Grid Naming Service - Performs name resolution

that start user resources (database, SCAN, listener etc).

http://rafik-dba.blogspot.com/2019/02/oracle-rac-startup-sequence.html

http://oracle-help.com/oracle-rac/rac-11gr2-clusterware-startup-sequence/