75 ways to demystify DB2 #46: Techtip : What Happens at DB2 Instance Startup?

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When troubleshooting db2start related issues, we often hear this question - what exactly happens at DB2 instance startup?

db2start

• User command to start the db2 instance
• Checks for authorization by forking/exec db2chkau
• Checks for existence of db2nodes.cfg file
• Forks/exec db2star2 and waits for completion

db2star2

• Actual start process
• Checks authorization
• Creates the DBMS Memory set
• Checks licenses
• Forks/exec db2sysc and waits for completion

db2sysc – DB2 system controller

• Connects to the Instance shared memory already allocated
• Forks a db2sysc
• Renames the process to db2wdog
• Watchdog monitors the db2sysc process for abnormal termination

System controller process – db2sysc

• Starts db2gds (generic daemon spawner) to handle EDU creation

If DB2COMM is set,
> Start appropriate communication listeners

• db2ipccm, for local client connections
• db2tcpcm, for TCP/IP connections
• db2tcpdm, for TCP/IP discovery tool requests

Then an entry is written to the db2diag.log indicating successful start operation