Most computers, including large installations, have various means to protect the stored information from unauthorized access. This is particularly important in systems that are shared by many users. The first line of defense consists of validating the access rights of a particular user, completely disabling access to storage contents and preventing the usage of system utilities when a user's identity cannot be properly confirmed. This is accomplished through the so-called login screen depicted in
Fig. B.1. While the actual appearance may differ from system to system, the screen contains two fields that must be filled out. The first is the user identifier as assigned by the system administrator, which is ...