Solution : https://service.sap.com/sap/support/notes/542021 (SAP Service marketplace login required)
Key words : 
cd /sapmnt/<sapsid>chmod 755 globalchmod 644 global/dscdb6, terms dbatools db2uext rc=43 returncode reason, confchmod 755 global/init<dbsid>, installing admin tools, symptom db2uext2 terminates, admin tool patch, <sapsid>adm, db2uext2 returns, 6d patch 21, error code 43
Related Notes : 
       
| 538315 | Central SAP Note for DB6 Admin Tools | 
| 410252 | DB6: Installing the Latest 4.6D DB2 Admin Tools |