Some days ago my dad upgraded his Laptop from Ubuntu 18.04 to 20.04. After doing so the package gnome-control-center went missing. Because this is GNOME’s main interface to configure various aspects of the desktop, the computer was basically unusable. The settings could not be opened through the search function or the system tray menu. In fact you could not access the settings anywhere. Because I spent quite some time fixing the problem without a reinstallation, I decided to share my solution. It may nor may not help someone in the future.

As is so often, I first took a look into the logs. Because systemd has its own logging system called the journal; running a separate logging daemon is not required. Using journalctl -e I discovered that the package gnome-control-center seemed to be missing. So I tried to install it via apt, which raised an error:

$ sudo apt install gnome-control-center
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 colord : Depends: libsane1 (>= 1.0.24) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

So I tried to install libsane1, which also failed:

$ sudo apt install libsane1
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 libsane1 : Depends: libsane-common (= 1.0.27-1~experimental3ubuntu2) but 1.0.27+git20180317-xenial0 is to be installed
            Recommends: sane-utils (>= 1.0.27-1~experimental3ubuntu2)
E: Unable to correct problems, you have held broken packages.

I tried to reinstall the whole package:

$ sudo apt --reinstall install sane simple-scan
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 sane : Depends: libsane1 (>= 1.0.24) but it is not going to be installed
 simple-scan : Depends: libsane1 (>= 1.0.24) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Without any luck. Also dpkg did not yield anything useful:

$ sudo dpkg --configure -a
foo@foo:~$ sudo apt-get install -f
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

I searched for the problem and found a matching bug in the official issue tracker of Ubuntu. As it turned out, the problem was caused by non-default PPA’s. In this case the Laptop is running a customized version of Ubuntu by Tuxedo. This distro uses it’s own PPA’S and caused the problem. The proposed solution :

$ sudo apt-get install libsane1/bionic libsane-common/bionic sane-utils/bionic

did not work me. Instead I tried to use Aptitude:

$ sudo aptitude install gnome-control-center

Aptitude does not give up so quickly and offers more options in dealing with dependencies. It was able to resolve the dependency conflict, so that gnome-control-center was installed successfully.

If you encounter problems while installing any package, try to use Aptitude instead of apt.