n                 Successful completion. The function returns a
                      non-negative integer shared memory identifier.

    -1                Indicates an error. The function sets errno to one
                      of the following values:

                      o  EACCESS - A shared memory identifier exists
                         for the key, but the operation permission as
                         specified by the low order 9 bits of shmflg
                         are not granted.

                      o  EEXIST - A shared memory identifier exists for
                         a key but ((shmflg & IPC_CREAT) &&
                         (shmflg & IPC_EXCL)) is non-zero.

                      o  EINVAL - The value of size is either less than
                         SHMMIN, greater than the SHMMAX, or a
                         shared memory identifier exists for a key, but
                         the size is greater than the size of that
                         segment.
                         With current implementation SHMMIN is defined
                         to 1 byte and SHMMAX is defined to 512 MB.

                      O  ENOENT - A shared memory identifier does not
                         exist for a key and (shmflg & IPC_CREAT)
                         is equal to zero.

                      O  ENOSPC - A shared memory identifier is to be
                         created but the system-imposed limit on the
                         maximum number of allowed shared memory
                         segments system-wide is exceeded.

                      o  EVMSERR - OpenVMS specific non-translatable
                         error code.