Monitor not detected by gnome-control-center

[miguelquiros]

 affects gnome-control-center

When trying to change monitor resolution via System Tools ->
Preferences -> Settings and then Devices -> Screen Display, a message
appears saying "Could not get screen information" and I cannot change
the monitor resolution or configure a second external monitor or
anything of the like.

On the other hand, I can use in a terminal the xrandr command and it
works perfectly, so I can configure the displays via this command.

If I start gnome-control-center from the command line in a terminal, I
can see the message:

Error calling GetCurrentState:
GDBus.Error:org.freedesktop.DBus.Error.NameHasNoOwner: Name
"org.gnome.Mutter.DisplayConfig" does not exist

I do not know if this error message may be related with the
malfunction
of the program.

The bug has started after some software upgrade, but I am not able to
remember which packages were updated at that time, in particular I do
not know if gnome-control-center itself was updated at that moment.

Ubuntu release is 18. gnome-control-center is 1:3.28.2
--
Miguel Quirós Olozábal
Departamento de Química Inorgánica. Facultad de Ciencias.
Universidad de Granada. 18071 Granada. SPAIN.
email: mquiros<at>ugr<dot>es
       mquiros<arroba>ugr<punto>es

[miguelquiros (mquiros)]

As the reported error message seems to point to mutter (I am using compiz), I start mutter issuing

mutter --replace &

And after this, I enter gnome-control-center, then the monitor is detected and its configuration is accessible. But this means stopping using compiz ...

Googling here and there, I have found that monitor configuration is accessible via unity-control-center but cheating with a variable in the environment, the command is:

XDG_CURRENT_DESKTOP=Unity:Unity7:ubuntu unity-control-center &

If the variable is not set, very few options are available under unity-control-center, in particular not the monitor. Well, at least it is a more or less acceptable workaround (I have put it in a script for not needing to remember the full command).