Before you submit any job involving CICS® VR undo logging, you need to specify the CICSVR_UNDOLOG_PREFIX (prefix) parameter in the active IGDSMSxx member of SYS1.PARMLIB. The default undo log is used if a submitted batch job does not match with any undo log associations that you have defined.
You can only define one default undo log for the system. If you want to use further undo logs, create undo log associations, as described in the CICS VR User's Guide. The extra undo logs that you name in undo log associations do not need to be defined in SYS1.PARMLIB.
The default undo log must only be used by CICS VR undo logging. No other applications, such as forward recovery logging, writes to this log stream.