Problem
In some cases, the master claims that it still needs to be joined to the domain.
root@ucs-mas-01:~# univention-run-join-scripts
univention-run-join-scripts: runs all join scripts existing on local computer.
copyright (c) 2001-2017 Univention GmbH, Germany
The system hasn't been joined yet. univention-run-join-scripts can only be
used after an initial, successful join. You should run univention-join instead.
root@ucs-mas-01:~# univention-check-join-status
Error: The system isn't joined yet
Solution
In a pure UCS domain, the DC master is not joined, but if this error occurs, the file /var/univention-join/joined is missing (e.g. an incorrect restore or accidental deletion).
Create the missing file with and everything works as it should again.
touch /var/univention-join/joined