System message process (SYSMSG) and related FM headers
The system message process is indicated by a process name in the ATTACH FM header.
Input system messages are routed to the master terminal operator when no ATTPRN is supplied in the ATTACH or SYSERROR FM header for a SYSMSG. This routing is accomplished by converting the incoming SYSMSG into IMS system message DFS2072. If an ATTPRN value is supplied, it becomes the IMS input message destination transaction code or LTERM name. The system message process cannot be used to access the IMS command processor.
A reply can result from an input SYSMSG if the ATTPRN value supplied is for an IMS transaction. This reply is returned through ISC edit or MFS, depending upon the output component definition.
IMS inserts system messages into IMS message queues using a default MFS MOD name. These messages are formatted as defined by the MOD during output to a component defined with MFS DPM. These MODs and associated DOFs are contained in the MFS format library.
- IMS broadcast messages
- System messages that IMS sends after sending a response to input. These system messages can occur instead of the application sending a reply (for example, when an abnormal termination occurs). IMS system messages directly solicited by an IMS command are sent as normal replies. Other system-generated messages can result from error conditions. These messages are converted to exception responses to the input transaction and are sent as error messages using the error recovery process (ERP).
MFS might edit an output SYSMSG, depending on the output component definition and whether the reply was inserted with an MFS MOD name.
Messages sent to or received by SYSMSG can include either the SYSSTAT or SYSERROR FM header. The SYSSTAT FM header is assumed by the receiver if no header is supplied by the sender. IMS can receive either header, and attaches a prefix to each header with IMS message number DFS2072 (if the message is to be sent to a master terminal operator). IMS sends broadcast output using the SYSSTAT header. All other IMS system messages sent as SYSMSG use the SYSERROR header. If the ATTACH ATTRDPN or ATTRPRN parameters are supplied on an input message that results in SYSMSG output, these parameters are included in the output SYSERROR FM header to be used by the receiver's SYSMSG process. The ATTACH ATTRDPN and ATTRPRN parameters are not sent for an IMS output SYSMSG.
Single-segment system messages created within IMS are 79 characters or less in length. Multisegment messages created within IMS can be greater than 79 characters in length, but each segment has a 79-character maximum length.
System messages created by input to the ISC SYSMSG process for output to the master terminal create single- and multisegment output messages. System messages created by input to the ISC SYSMSG process in which ATTPRN and ATTDPN are specified must have a MID capable of handling multisegment messages with a minimum of five segments.