3.4. Permission concept#
The permission concept in UCS specifies who can read and write domain data. Permissions apply to objects in the domain database like users and systems alike. Policies assign custom permissions to objects. UCS applies default permissions for systems and predefined users and groups.
3.4.1. System roles#
UCS system roles imply certain permissions on domain data. Only the Primary Directory Node can write data to the domain database. All other system roles have read-only access. Nevertheless, other systems or users have write permissions for certain operations affecting themselves and they run them on the Primary Directory Node.
For example, when a UCS system joins the domain or an administrator installs an app, the events trigger write operations on the Primary Directory Node.
3.4.2. Administrator and root#
Some user accounts also have implicit permissions on domain data and systems. A UCS system knows two administrative user accounts: Administrator and root.
The user account Administrator is the first domain user and has all domain permissions. The Administrator user account has permission to join systems to the domain and can work with all modules in the UCS management system. The account can only be defined once in the domain and must never be renamed.
The Administrator account is only defined once per domain during the installation of the Primary Directory Node. The account password is set during installation.
Think of Administrator as the primary administrative account for the UCS domain.
The user account root is the superuser on the local UCS system and has the user ID of
0. It has all permissions and is equivalent to the root account known from other GNU/Linux systems.
The root account is defined and the password is set during installation of every UCS system. The account is only for the local UCS system. On other UCS systems administrators should—of course—define different passwords for each root account.
Think of root as the primary administrative account for the local UCS system.
The root account has no permissions and is no valid account in the domain context. The account root must not be created as domain account.
3.4.3. Domain users and admins#
To simplify the assignment of certain user permissions, UCS has two default user groups in the domain that differ fundamentally: Domain Users and Domain Admins.
- Domain Users
UCS assigns every user to the user group Domain Users per default. The group identifies the user account as belonging to a person. The user account only has a minimal set of permissions in the domain.
For example, user accounts in the group can read the domain database, but can’t view password hashes. Additional apps in the domain such as UCS@school or Fetchmail can alter read and write permissions for users and systems. User accounts in the Domain Users group also can’t sign in to UCS systems for a remote shell by default. The UCS management system yields no modules for them either.
- Domain Admins
UCS creates one user account called Administrator during the installation of the first UCS system (Primary Directory Node) in a domain. It’s the first user account and has all permissions for the domain. The Administrator user account is member of the Domain Admins group.
Users in Domain Admins group have all domain permissions just like the Administrator account. To join a UCS system to the domain, administrators need a user account that’s member in the groups Domain Admins and DC Backup Hosts.
- Subsequent domain joins with univention-join
For more information about subsequent domain joins in 
3.4.4. Machine account#
All systems part of the domain are actors in a domain like users. Each system has its own account in the domain database. The account is called machine account. Depending on the type of system they have different permission sets.
UCS systems can read data from the domain database with their machine account. Every machine account has assigned the following default permissions in the UCS domain:
The UCS system can read all object information and password hashes for accounts from the domain database. Apps like UCS@school and Fetchmail limit the read permissions.
The UCS system can write only information to the domain database that’s associated with its account, for example the version of the installed UCS or other apps.
In addition to the permissions defined for system roles and predefined groups, UCS offers policies for more fine-grained control on administrative settings.
Policies are administrative settings to help administrators with infrastructure management that can be assigned to objects in the domain database. Policies use the inheritance principle as it’s known from object oriented software programming. Inheritance allows to set policies to one object in the structured domain database. The policy then applies to all objects that are organized in the structure below.