2844715 - DB6: "Update DBM cfg SYSADM_GROUP errcode = 8" on db2icrt at the step of Create Instance using SWPM OR when running db2iupgrade, error with /dev/null

Scenario 1

During the new installation using SWPM, the following error is raised at the step of CreateInstance:

ERROR 2019-09-17 13:41:46.517 (root/sapinst) id=controller.stepExecuted errno=FCO-00011
The step CreateInstance with step key |NW_ABAP_OneHost|ind|ind|ind|ind|0|0|NW_Onehost_System|ind|ind|ind|ind|onehost|0|NW_CreateDBandLoad|ind|ind|ind|ind|createdbandload|0|NW_CreateDB|ind|ind|ind|ind|createdb|0|NW_DB6_DB|ind|ind|ind|ind|db6|0|NW_DB6_CreateDB2Instance|ind|ind|ind|ind|NW_DB6_CreateDB2Instance|0|CreateInstance was executed with status ERROR (Last error reported by the step: Executable </db2/db2abc/db2_software/instance/db2icrt> has Returncode <1>. See db2icrt.log for details).

db2icrt trace file shows the following information:  
=========
Program name = db2idbm

Instance home dir = /db2/db2abc, Sysadm group = dbabcadm
Instance type = 1, Auth type = SERVER_ENCRYPT

DB21015E The Command Line Processor backend process request queue or input
queue was not created within the timeout period.
Update DBM cfg SYSADM_GROUP errcode = 8
DBI1281E The database manager configuration file could not be
initialized.

Explanation:

An error occurred when attempting to initialize the database manager
configuration file. A database manager instance could not be created or
upgraded.
=========

******************************************************************

Scenario 2

During DB2 upgrade while executing instance upgrade command 
/db2/db2<SID/db2_software_<DB2_version>/instance/db2iupgrade -u db2<SID> db2<SID> encounters an issue
The db2 set log shows

ERROR: 1> /dev/null
1> /dev/null
1> /dev/null
Program name = db2idbm
Instance home dir = /db2/db2<SID>, Sysadm group = db<SID>adm
Instance type = 1, Auth type = SERVER

DB21015E The Command Line Processor backend process request queue or input
queue was not created within the timeout period.
Update DBM cfg SYSADM_GROUP errcode = 8
DBI1281E The database manager configuration file could not be
initialized.

SAP on IBM Db2 for Linux, UNIX, and Windows

FCO-00011, CreateDB2Instance, DB21015E, Update DBM cfg, SYSADM_GROUP, errcode = 8, DBI1281E , KBA , BC-DB-DB6-INS , Installation SAP System , Problem