The system programmer at your installation codes installation exit routines that gain control when the system issues certain messages. A WTO installation exit can change routing codes, descriptor codes, and message texts, as well as perform other message processing; it can override MPF processing. Information about coding these installation exits appears in z/OS MVS Installation Exits.
The most effective message control involves coding and installing the installation exit IEAVMXIT, which can gain control when any WTO or WTOR message is issued.
To learn whether IEAVMXIT is active or not, issue the CONTROL M,REF command. The system displays (in the entry area) the status of the action message retention facility, the status of installation exit IEAVMXIT, and the limit of the number of WTO and WTOR buffers.
Your installation might have other exit routines to process messages. MPFLSTxx parmlib members contain the IDs of messages and the installation exits that process these messages. To activate processing by these installation exits, see Controlling the message processing facility (MPF).
Use the UEXIT operand on the CONTROL command to control whether the installation exit IEAVMXIT is active.
Example:
CONTROL M,UEXIT=NThe effect of the command lasts only for the duration of the IPL.