https://www.ibm.com/docs/en/ims/15.2.0?topic=parameters-fesexit-parameter-procedures
IMS 15.2 - System definition - FESEXIT= parameter for procedures
Use the FESEXIT=N|Y parameter in procedure to specify whether the Front End Switch exit routine, DFSFEBJ0, is to be loaded by the IMS system.
imssystemdefinitionparameterprocedures