Optionally, a maximum of eight user header labels (UHL1 to UHL8) can appear on the tape immediately following the data set header labels. These labels contain user-specified data that can be made available to your program for processing.

If you want the system to write user header labels or to make user header labels available to your program, you must specify SUL on the DD statement and specify the address of a user header label routine in the DCB exit list. (The exit list can address several user header label routines, that is, routines that process input user header labels and create output user header labels.) The DCB exit list is described in z/OS DFSMS Using Data Sets.