In order for this function to be available, VLF must be active and the active COFVLFxx member of SYS1.PARMLIB must include statements defining the VLF classes used for the mapping. Update the COFVLFxx member of SYS1.PARMLIB as follows:

CLASS NAME(IRRGMAP)        /* GMAP table for z/OS UNIX System Services   */
EMAJ(GMAP)                 /* Major name = GMAP                          */
CLASS NAME(IRRUMAP)        /* UMAP table for z/OS
UNIX System Services   */
EMAJ(UMAP)                 /* Major name = UMAP                          */