Each time when I want to close terminal there is a popup with question "Close this terminal?" because some process is running in terminal. I don't care about this process. How to prevent terminal from showing this popup?
In 16.04 you'll find that choice in dconf-editor. You can install it, if necessary, with
sudo apt install dconf-editor
Then go to
org -> gnome -> terminal -> legacy
You will have to install
gconf-editor first. Just open the terminal using Ctrl+Alt+T and type the following command:
sudo apt-get install gconf-editor
After that, hit Alt+F2 or open the Dash and type
gconf-editor and the configuration editor window will appear. Then you go to Apps→Gnome-terminal→global and uncheck the option
Just press Ctrl + C to cancel any background process that may be running and then you can close the terminal without the popup showing up.
You can affect your system by closing the terminal with background processes running. A good example is if there is an update or upgrade running, the apt command can get locked up and you may start getting these errors:
E: Could not get lock /var/lib/dpkg/lock - open (11 Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/) is another process using it?
Luckily, they have been solved in this question.
That is just an example of what may happen if you close the terminal when a background process is running. Other things may happen depending on the process itself.