I was unable to open the settings tab of my ubuntu 18. This seems to be a very common issue as I found various threads on it with solutions ranging from asking to remove external ppas, reinstalling gnome-control-center etc. However none of this worked.
Finally I ran gnome-logs from the terminal and saw the detailed segmentation fault error under the System tab:
gnome-control-c[28768]: segfault at fffffff8 ip 00007fe6cc71c8a0 sp 00007ffdf553f9e0 error 4 in libc-2.30.so[7fe6cc6a4000+178000]
On searching for error 4 libc along with gnome-control-center segmentation fault, I found the following page which finally solved the issue for me, at least temporarily.
https://bugzilla.redhat.com/show_bug.cgi?id=1668792
Removing the "user" file from .config/dconf folder made gnome-control-center work again!
