CLT—command list table

The command list table (CLT) is used by the extended recovery facility (XRF) and contains a list of MVS™ system commands and messages to the operator, to be issued during takeover. Typically, the function of these commands is to tell alternate systems to take over from their active systems in the same MRO-connected configuration.

The command list table also contains the name of the alternate system, with the jobname of the active system that it is allowed to cancel. (See DFHCLT TYPE=LISTSTART FORALT operand.) This provides a security check against the wrong job being canceled, when the alternate system takes over.

In addition, the DFHCLT TYPE=INITIAL macro gives JES routing information, needed to send cancel commands to the appropriate MVS system. If you are using XRF, you must have a CLT: it is used only by the alternate CICS® system.

For security reasons, link-edit the CLT into a library authorized using APF. For virtual storage constraint relief considerations, link-edit using a MODE control statement specifying AMODE(31),RMODE(ANY). The table should be link-edited as reentrant. The CLT is not loaded into the CICS nucleus.

Your CLT can contain the following statements:
  • DFHCLT TYPE=INITIAL
  • DFHCLT TYPE=LISTSTART
  • DFHCLT TYPE=COMMAND
  • DFHCLT TYPE=WTO
  • DFHCLT TYPE=LISTEND
  • DFHCLT TYPE=FINAL (see TYPE=FINAL (end of table))
Note: Although the CLT may be shared by a number of alternate systems, take care that MVS is not given too many redundant commands during takeover. For example, in multiregion operation and using one CLT with commands for several regions, region 1 would send valid commands to other regions, but they would in turn send redundant commands to region 1 and to each other.