(Split off bug 6192)
Distributions are trying to simplify X authentication and discourage running things as root. As such some X servers are configured to only allow connections from a specific user:
> $ xhost
> access control enabled, only authorized clients can connect
This breaks our installer and tl-setup as they run as root and therefore cannot access this X server. Bug 6192 makes sure we fall back to text mode when we detect this problem, but ideally we would like to have a graphical installation for these systems as well.
Note that this is mostly seen with Xwayland, but it could happen for any X server.
Also note bug 6192, comment 9 which states that Xwayland might start allowing root in the future.
And GNOME has now pushed a commit allowing sudo X11 stuff: