You can halt VTAM® using the HALT or HALT QUICK commands. When VTAM is halted, all of its resources are deactivated, and all sessions involving those resources are terminated. Additionally, if the VTAM being halted is an intermediate routing node, any sessions passing through that VTAM are disrupted. Sessions running under the IBM® Network Routing Facility program might be disrupted if the VTAM host is halted. This is true in any situation where the session ends are not in the host subarea. If the HALT or HALT QUICK commands do not run properly, the operator can cancel VTAM.

The CDLINK operand for the HALT command is the same as for the VARY INACT command, except that the cross-subarea links to which it applies are determined when the HALT command is entered and are not redefined as the domain contracts. That is, the CDLINK operand applies to all cross-subarea SDLC links between NCPs that are cross-domain at the time the HALT command is entered.

Except for channel links, all other cross-subarea links (those that are entirely within the domain at the time the HALT command is entered) remain active during and after the halt, regardless of how CDLINK is specified. That is, their final status does not depend on whether the links and their link stations were automatically, directly, or indirectly activated. This allows sessions using that link to remain active. It also allows nondisruptive, simultaneous NCP deactivations, regardless of how the communication controllers are connected within the domain. Cross-subarea channel links are always deactivated during a VTAM halt.

The HALT command notifies application programs within the VTAM subarea of the domain shutdown and waits for them to close their ACBs. Intermediate routing node traffic passing through the VTAM being halted will be disrupted without notification.

New sessions are not permitted and new ACBs cannot be opened for any resources of the host that have received a HALT command. Except for this restriction, application programs of the host that have received a HALT command can continue their current operations. Any pending-active sessions are terminated, but active sessions remain active. After all application programs have stopped using VTAM services (that is, after they have closed their ACBs), processing is the same as for the HALT QUICK command.

During a normal halt, you can monitor the shutdown of the domain by displaying the status of application programs and other logical units. The VARY TERM command can be used to terminate sessions, and, if necessary, to speed the processing of the HALT command.

The HALT QUICK command can also be used at this time, if necessary, to speed halt processing. The HALT QUICK command notifies application programs of the domain shutdown and then proceeds with the equivalent of the VARY INACT,TYPE=IMMED command for each major node. All active LU-LU sessions are disrupted. After VTAM has received a HALT QUICK command, the only VTAM commands that can be used are DISPLAY commands, VARY TERM commands (to terminate sessions), and VARY INACT,TYPE=FORCE commands (to force the deactivation of resources).

If during HALT QUICK processing, after all the major nodes are inactive, any application programs have not yet closed their ACBs, VTAM displays a message listing the names of these application programs. Because VTAM cannot shut down the domain until all application programs have been disconnected from VTAM, you might want to speed up the halt process by canceling the jobs of application programs with open ACBs. The HALT QUICK command can prevent an application program from using VTAM services, but VTAM cannot force the program to disconnect itself from VTAM. When the operator cancels an application program, the host operating system disconnects it from VTAM.