| ### Establishing Trust Relationships Use the registry connect command to establish direct trust and transitive trust relationships. Note that, although you can create a direct trust relationship between any two cells, you can create a transitive trust relationship only for those cells connected by a transitive trust path. This command creates two special accounts: one in your cell's registry to represent the foreign cell, another in the foreign cell's registry to represent your cell. The command creates the accounts' principals at the same time. Once the trust relationship is established, users in the foreign cell can log into accounts in the local cell and vice versa. You control foreign principals' access to specific objects with ACL entries, just as you do for principals in the local cell. When the accounts are created, the registry connect command performs two tasks that you should be aware of. First, it automatically generates one password that is shared by both accounts. This means that users who log into a cell with which their cell has a trust relationship are seen as the same principal and share the same password. Second, the registry modify command generates a UNIX number that is shared by all principals that are in a given foreign cell. This shared UNIX number helps prevent collision between the UNIX numbers of local and foreign principals when objects on a local machine are accessed. Within the registry and for the purposes of network access, principals are identified by a UUID that represents their fully qualified names; for example, /.../dresden.com/dce/users/mahler for the principal mahler. However, the local operating system on a local machine identifies principals by UNIX number. Because UNIX numbers are not required to be unique across cells, it is possible for two principals from different cells to have the same UNIX number. Thus, a foreign principal that is accessing files in the local cell could have the same UNIX number as the local principal and be seen by the local system as the owner of the local user's files on the local machine. Creating a UNIX number that is applied to every principal from a given cell that accesses the local cell prevents this from occurring. However, you need to be aware that, because the foreign users all have the same UNIX number, the very feature that prevents them from accessing the local user's files allows them to access each other's files. Because each user from the same foreign cell is seen as the same user, every file on the local machine that is owned by a foreign user can be accessed by every other foreign user from the same foreign cell. ###