Signing on multiple times

Users can concurrently sign on to one or more terminals. These terminals can be a combination of both static and dynamic terminals.

For both static and dynamic VTAM® terminals, you must specify the EXEC parameter, SGN=M (multiple signons enabled).

For dynamic terminals, the name of the user structure that represents the user to IMS must be unique. You can use one of four methods to make the user structure unique:
  • Use the Signon exit routine (DFSSGNX0) to return a 1- to 3-byte suffix to the user ID. The total length of the user ID plus the suffix cannot exceed eight characters.

    Recommendation:  Use a naming convention that ensures unique user IDs. For example, you can create suffixed user IDs using the Signon exit routine (DFSSGNX0), and check the uniqueness of these user IDs by using IMS Callable Services.

    Recommendation:  If you are operating in a sysplex environment, create a naming convention that ensures unique user IDs across the IMSplex by creating a suffix from the following:
    • As the first part of the suffix, the Signon exit routine can attach the unique part of the IMS system identifier, which is specified on the IMSID parameter, to the user ID.
    • As the second part of the suffix, use IMS Callable Services to choose an available value for the user on that IMS system.
    Example: A user with a user ID of USER signs on to IMSA. A unique suffix of A1 is created through this two-step process:
    1. The Signon exit routine appends the A from IMSA to the user ID.
    2. The Signon exit routine invokes IMS Callable Services. The exit routine then appends a 1, representing the first user named USER to sign on to IMSA.
    In this example, user IDs must be less than six characters in length.
  • Use the Signon exit routine to specify that the user structure name is the same as the node name.
  • Use the Signon exit routine to specify a name that is unrelated to the user ID or the node name.
  • Specify a user descriptor name that is the same as the node name, causing the name of the user structure to be the same as the node name. You can do this by using one of the following methods:
    • Enter signon data that contains the user descriptor name.
    • Use the Signon exit routine to specify the node user descriptor.
    • Specify no user descriptor and let IMS use the node user descriptor by default.

Unless you specify SGN=M to enable multiple signons, the user ID for a dynamic user must be unique. If the user ID is used as the user-structure name, it must be unique, regardless of whether you specify SGN=M. If the user ID is not used as the user-structure name (for example, by using the Signon exit routine), you must specify SGN=M for multiple signons.

Recommendation:  Assigning a single name to an IMS user is useful in determining output status. If you use multiple names for individual users (for example, when the Signon exit routine assigns them), you must provide a means to determine the user names that are created by signons.

Restriction:  You cannot use the same name for a dynamic LTERM and a static LTERM that is defined during system definition.