There are many question about this topic and all of them has same kind of answer.
With dpkg configuration:
sudo dpkg-reconfigure keyboard-configuration
With dconf editor:
gsettings set org.gnome.desktop.input-sources xkb-options "['terminate:ctrl_alt_bksp']"
source: How can I enable Ctrl+Alt+Backspace?
But recently I installed Ubuntu 17.10 and its environment is GNOME. I tried both ways but none of those are working for me.
Can anybody help?
EDITED:
There is an another method of dontzap
. But it is a bug or not available.