Publisher Summary After creating the user IDs, control must be established over their access to individual nodes and the expanded network. The authentication sequence depends on four parameters—the access batch or interactive, the communication medium being used, the Safeguard TERMINAL controls being used, and the personality of the HP NonStop server being used. The combinations of these parameters determine which path the user will take through the process of authenticating the user's identity. The Guardian system requires that users must logon to the system with a valid user ID or alias and a password. TACL is the command interpreter used with the Guardian system. The logging on process calls the USER_AUTHENTICATE_ routine. During this system call a PRELOGON message is sent to CMON, if it is running. If the PRELOGON request passes the CMON rules, a LOGON request is sent to CMON, if it is running. The USER_AUTHENTICATE_ procedure will utilize the Safeguard facility, SZSMP, if Safeguard software is on the system. SZSMP evaluates both the Safeguard configuration and the User Record attributes to determine if the access will be granted. Based on the Safeguard configuration, SZSMP also determines whether or not the logon will be audited. If the USER_AUTHENTICATE_ procedure does not exist in the system library, TACL calls the VERIFYUSER system procedure.