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

Technical Blog Post


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


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


  • 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


  • 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

[{"Business Unit":{"code":"BU029","label":"Data and AI"}, "Product":{"code":"SSEPGG","label":"DB2 for Linux- UNIX and Windows"},"Component":"","Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"","Edition":""}]