You must create users for iucvconn_on_login.
Each target system to which you want to connect with iucvconn_on_login requires a separate Linux user on the terminal server. The user ID must match the z/VM® user ID of the target system.
You might be using an external security manager for your z/VM system, for example, Resource Access Control Facility (RACF®). If so, you can set up Linux to use the external security manager for authentication. See Security on z/VM, SG24-7471 for more information.