The operating system is designed to support the X/Open UNIX95 Specification for portability of UNIX-based operating systems. Many new interfaces, and some current ones, have been added or enhanced to meet this specification and AIX has become even more open and portable for applications.
At the same time, compatibility with previous AIX releases is preserved. This is accomplished by the creation of a new environment variable, which can be used to set the system environment on a per-system, per-user, or per-process basis.
The default AIX environment is one that maintains compatibility with previous AIX releases. To obtain an environment designed to conform to the UNIX95 specification, the environment variable XPG_SUS_ENV must be assigned the value ON. If XPG_SUS_ENV is set to any other value, or is unset, the default AIX behavior will be used.
When XPG_SUS_ENV is set, every program in that environment will operate in the UNIX95-specified operating system environment. It is possible that some applications compiled for the AIX environment (perhaps for an earlier version of AIX) will not operate correctly when XPG_SUS_ENV is set.