* All roles are owned by the system user.
* The name of a role is unique across a single Arvados cluster.
* Roles can be both targets (@head_uuid@) and origins (@tail_uuid@) of permission links.
+* By default, all roles are visible to all active users. However, if the configuration entry @Users.RoleGroupsVisibleToAll@ is @false@, visibility is determined by normal permission rules, _i.e._, a role is only visible to users who have that role, and to admins.
+* By default, any user can create a new role. However, if the configuration entry @Users.CanCreateRoleGroups@ is @false@, only admins can create roles.
h3. Access through Roles
*can_manage* access to a user grants can_manage access to the user, _and everything owned by that user_ .
If a user A *can_read* role R, and role R *can_manage* user B, then user A *can_read* user B _and everything owned by that user_ .
+Modifying a role group requires *can_manage* permission (by contrast, *can_write* is sufficient to modify project groups and other object types).
+
h2(#system). System user and group
A privileged user account exists for the use by internal Arvados components. This user manages system objects which should not be "owned" by any particular user. The system user uuid is @{siteprefix}-tpzed-000000000000000@.