Connection to database when using username and password can fail with error SQL1639N The database server was unable to perform authentication because security-related database manager files on the server do not have the required operating system permissions.
This is caused by incorrect permissions and ownership of the following security files in ~/sqllib/security directory
These files should have root as owner and must have permission -r-s--x--x
Resolving The Problem
Change the owner of the files to root
Change the permission of the files to -r-s--x--x
Update the instance using db2iupdt
16 June 2018