Start session scripts cannot run interactively. A start session script runs in an environment created by Horizon and must obtain its input data from that environment.

Start session scripts gather input data from environment variables on the client computer. Start session environment variables have the prefix VDM_StartSession_. For example, the start session environment variable that contains the client system’s IP address is VDM_StartSession_IP_Address. You must ensure that a start session script validates the existence of any environment variable that it uses.

For a list of variables similar to start session environment variables, see Client System Information Sent to Remote Desktops.