In addition to giving you the tools to create sophisticated graphs, Cacti enables you to create users that are tailored specifically to their requirements. Each user has certain settings such as login actions, as well as graph viewing settings. There are also two levels of permissions control, realm permissions and graph permissions which enable you to control what the user can see and change.
Out of the box, there are two users that come with every Cacti installation. The “admin” user, is the main user that by default has access to see and change everything in Cacti. This is the user that you first login with in Cacti, and is probably a good idea to keep around unless you know otherwise. The second user is the “guest” user, which controls which areas/graphs are allowed for unauthenticated users. By default this user only has rights to view, but not change all graphs. This enables any unauthenticated user to visit 'graph_view.php' and view your graphs. This behavior can be changed by either changing the realm permissions for the “guest” user, or disabling the guest user altogether under Cacti Settings. By default in 0.8.7 and later, the “guest” user is not set in the setting, effectively disabling “guest” (Unauthenticated) access to Cacti.