The below issue has been observed in Oracle Database 12c (in specific 18.104.22.168) on AIX OS, when LOCK_SGA parameter is set.
ORA-27125: unable to create shared memory segment
IBM AIX RISC System/6000 Error: 1: Not owner
The OS user with which Oracle is installed must be missing some permissions.
Request the AIX admins to set the capabilities for the user in which Oracle is running.
To check whether capabilities is set or not, please issue the below command,
lsuser -a capabilities <DB User>