The problem is that I cannot start DB2 instance after installation, and get the error
The database manager shared memory set cannot be allocated.
SQL1220N error happens under two conditions.
1. Instance_memory is set to hard value that is too high to be allocated.
2. This error can also be seen even if the instance memory is already set to automatic. For example if the privileged value of zone.max-locked-memory is explicitly set in the operating system by the system administrator, then the same error can be seen during db2start. By default this is not set in the operating system.
Set the dbm cfg INSTANCE_MEMORY value to AUTOMATIC by issuing the following command from a DB2 Command Window as the instance owner:
db2 update dbm cfg using INSTANCE_MEMORY AUTOMATIC
Once this is done, then attempt to start your instance.
If INSTANCE_MEMORY is already set to automatic and you encounter the error again. Then either remove the capping from zone.max-locked-memory; or work with your system administrator to set the privileged limit for "zone.max-locked-memory" high enough for DB2 to start.