Solution : https://service.sap.com/sap/support/notes/407543 (SAP Service marketplace login required)
Key words : 
concerns 32-bit db servers, csh' scripts provided, environment variable extshm, environment variable 'extshm', csh' setenv extshm, multiple address spaces, terms memory allocation, maximum address space, usable address space, prerequisites 32-bit processes
Related Notes : 
       
| 174882 | Shared memory segment shortage on AIX | 
| 111876 | Installation of a 64 bit Informix Dynamic server | 
| 41360 | Database configuration using onconfig parameter |