Modifying and Controlling System Resources

You establish the initial settings of IMS resources during IMS system definition. The MTO, and other operators authorized to do so, can change various system resources using IMS commands.

"Modifying the Operating State of Specific IMS Resources" on page 422 describes how you can modify the operating state of specific resources using specific IMS commands.

"List of Commands with Similar Functions for Multiple Resources" on page 425 describes how many IMS commands perform similar control functions for different types of resources.

Related Reading: For details about the IMS commands, see IMS Version 9: Command Reference.

Modifying the Operating State of Specific IMS Resources

You can use certain commands to affect the operating state of specific resources, as described in the following sections.

Modifying Dependent Regions

Use the /ASSIGN command to modify the assignment of classes to regions. Do this to adjust the processing load among message regions.

Modifying Telecommunication Lines

Use the /RSTART command to start lines, lines and physical terminals, logical links, nodes, and users when you do not want to reset all associated conditions, such as a conversation or special operating mode. Use the /DEQUEUE command to discard response-mode output messages before you issue an /RSTART LINE command.

Modifying Terminals

Use the /ASSIGN LTERM command to modify the assignment of logical terminals to physical terminals or nodes. The new assignment remains in effect until the next cold start or until you issue another /ASSIGN command.

Use the /DEQUEUE command to discard response-mode output so that the /RSTART command can reset terminal response mode.

Use the /COMPT command for VTAM terminals (nodes) to notify IMS that a terminal component is operable or inoperable.

IMS provides a VTAM I/O timeout facility to detect VTAM hung nodes and determine what action, if any, should be taken. Use the /TRACE command to start and stop the VTAM I/O timeout facility. Use the /IDLE command to deactivate a node and the /ACTIVATE command to activate a node. Use the /DISPLAY command to display all nodes that have I/O outstanding for a time period greater than that specified during system definition.

Modifying Transactions

Use the /ASSIGN command to reassign the scheduling priorities established for transactions during system definition. The new assignments remain in effect until the next cold start or until you issue another /ASSIGN command.

In a shared-queues environment, you can use the /ASSIGN command to control which IMS subsystems can run certain types of transactions by assigning transactions to particular classes.

For example, you can define TRANA to class 4 on IMSA and to class 255 on IMSB and IMSC, so that only IMSA can run TRANA. If IMSA fails, you can reassign TRANA on either IMSB or IMSC to a class that these IMS subsystems can run.

Recommendation:

Do not use the /STOP TRANSACTION command to control which IMS subsystems can run certain types of transactions.

Modifying Databases

Use the /DBDUMP command to stop online update access to a database and produce an offline dump of the database.

Use the /DBRECOVERY command to stop all online access to a database. Use it to recover a database offline.

Normally, IMS switches to using the next OLDS when you enter the /DBDUMP or /DBRECOVERY command. This switch does not occur if you specify the NOFEOV keyword on either command.

Specify the GLOBAL keyword on the /DBDUMP command or /DBRECOVERY command to have the command apply to all subsystems sharing the database. The IRLM must be active if you use this keyword. The default is LOCAL, which specifies that the command applies only to the subsystem on which you enter the command.

You must restart IMS after you issue a command with the GLOBAL keyword.

Modifying ISC Users (Subpools)

Use the /ASSIGN command to change the assignment of a static LTERM to an ISC user (also called a subpool). The new assignment remains in effect until the next cold start or until you issue another /ASSIGN command.

Modifying ETO Users

For dynamic user IDs, use the /ASSIGN command to change the assignment of a user ID to another user or to an LTERM. The new assignment remains in effect until the next cold start or until you issue another /ASSIGN command.

Use the /DISPLAY USER DEADQ command to list all message queues that are eligible for dead letter status. IMS refers to data that cannot be delivered as a dead letter. Use the /ASSIGN command to assign a dead letter queue to another user ID. Use the /DEQUEUE command to discard a dead letter queue.

In a shared-queues environment, use the /DISPLAY QCNT MSGAGE command to determine which messages, if any, are eligible for dead letter status.

Modifying MSC Resources

Use the /MSVERIFY command to verify the consistency of MSC system identifications (SYSIDs) and logical link paths (MSNAMEs) across two systems. You can use the /MSASSIGN command to change the assignment of MSNAMEs and SYSIDs to logical links.

All changes made by an /MSASSIGN command remain in effect until the next cold start or until you issue another /MSASSIGN command.

After using the /MSASSIGN command, you should use the /MSVERIFY command to ensure that the assignment produced a valid configuration.

Modifying Security Options

Use the /CHANGE command to update a current password with a new password. The current password must be known to IMS.

Restriction:

IMS does not allow different user IDs to use the same passwords.

Use the /MODIFY PREPARE RACF and /MODIFY COMMIT commands to reinitialize RACF information if you are not using a RACF data space. If you are using a RACF data space, use the RACF SETROPTS RACLIST command rather than the IMS /MODIFY command.

Use the /DELETE command to delete terminal or password security for the specified system resource.

Use the /SECURE APPC command to control the RACF security level for input from LU 6.2 devices. Use the /DISPLAY APPC command to show the security level that is currently in effect. When IMS starts, the default is full security.

Use the /SECURE OTMA command to control the RACF security level for input from OTMA clients. Use the /DISPLAY OTMA command to show the security level that is currently in effect. When IMS starts, the default is full security.

Modifying Conversations

Use the /DISPLAY CONV command to show the status of all conversations, held or active. You can terminate a conversation if necessary with the /EXIT command, but you should do this only after warning the end user.

Modifying Subsystems

Use the /CHANGE command to delete an invalid network identifier (NID). If you need to disconnect from a specific subsystem, use the /STOP command. If the /STOP command does not work, use the z/OS MODIFY command.

List of Commands with Similar Functions for Multiple Resources

You can use many IMS commands to perform similar control functions for different types of resources. The tables in this section show the relationship between these commands and resources, and provide answers to a series of specific questions. For example, after a command is issued, can a resource:

• Receive input?

• Send output?

• Perform output message queuing?

The following tables show what IMS commands affect certain resources. The resources are:

• Telecommunications Line, Physical Terminal, or Node Resources (Table 24-1)

  Table 24-1. IMS Commands That Affect Telecommunications Line, Physical Terminal, or Node Resources

  IMS Command	Receive Input	Send Output	Output Message Queuing
  /ASSIGN	Y	Y	Y
  /LOCK	N	N	Y
  /MONITOR[a]	Y	N	Y
  /PSTOP[a]	N	N	Y
  /PURGE[a]	N	Y	Y
  /RSTART[a]	Y	Y	Y
  /START	Y	Y	Y
  /STOP	N	N	Y
  /UNLOCK	Y		Y

  
  

  ^[a] /MONITOR, /PSTOP, /PURGE, and /RSTART refer to the telecommunication line or physical terminal, not to the node.

• Logical Terminal Resources (Table 24-2)

  Table 24-2. IMS Commands That Affect Logical Terminal Resources

  IMS Command	Receive Input	Send Output	Queuing from Other Terminals	User
  /ASSIGN	Y	Y	Y	Y
  /LOCK	N	N	N
  /PSTOP	N	N	Y
  /PURGE	N	Y	N
  /RSTART				Y
  /START	Y	Y	Y	Y
  /STOP	N	N	N	Y
  /UNLOCK		Y	Y

  
  

• Logical Link Resources (Table 24-3)

  Table 24-3. IMS Commands That Affect Logical Link Resources

  IMS Command	Receive Input	Receive Output
  /PSTOP	N	N
  /RSTART	Y	Y

  
  

• Logical Link Path Resources (Table 24-4)

  Table 24-4. IMS Commands That Affect Logical Link Path Resources

  IMS Command	Queue Primary Requests Not Continuing Conversation	Transmit Queue Message to Partner Systems
  /ASSIGN	Y	Y
  /PURGE	N	Y
  /START	Y	Y
  /STOP	N	N

  
  

• Transaction Resources (Table 24-5)

  Table 24-5. IMS Commands That Affect Transaction Resources

  IMS Command	Message Scheduling by Transaction	Message Queuing by Transaction
  /ASSIGN	Y	Y
  /LOCK	N	Y
  /MSASSIGN	Y
  /PSTOP	N	Y
  /PURGE	Y	N
  /START	Y	Y
  /STOP	N	N
  /UNLOCK	Y	Y

  
  

• Transaction Class Resources (Table 24-6)

  Table 24-6. IMS Commands That Affect Transaction Class Resources

  IMS Command	Transaction Scheduling by Class
  /ASSIGN	Y
  /MSASSIGN	Y
  /START	Y
  /STOP	N

  
  

• Program Resources (Table 24-7)

  Table 24-7. IMS Commands That Affect Program Resources

  IMS Command	Execute
  /ASSIGN	Y
  /LOCK	N
  /START	Y
  /STOP	N
  /UNLOCK	Y

  
  

• Database Resources (Table 24-8)

  Table 24-8. IMS Commands That Affect Database Resources

  IMS Command	Use
  /ASSIGN	Y
  /START	Y
  /STOP	N
  /UNLOCK	Y

  
  

• Subsystem Resources (Table 24-9)

  Table 24-9. IMS Commands That Affect Subsystem Resources

  IMS Command	Attach
  /ASSIGN	Y
  /START	Y
  /STOP	Y

  
  

Telecommunications Line, Physical Terminal, or Node Resources

Logical Terminal Resources

Logical Link Resources

Logical Link Path Resources

Transaction Resources

Transaction Class Resources

Program Resources

Database Resources

Subsystem Resources