The AIX version of Oracle 11g was built on AIX 5 so when you try to create an Oracle database using the Database Configuration Assistant, aka, ‘dbca’, you may get the ORA-27173 “unable to attach to shared memory” error. Oddly enough this has to do with the time zone (TZ) setting. You see, dbca has no concept of the Olsen Time Zone ids, it is expecting what AIX 5 used. So you need to explicitly set the time zone environment variable (TZ).
AIX 6 had my TZ set to “America/New York”. For Oracle’s dbca to work, I had to set TZ to “EST5EDT”.