Some keyboard shortcuts no longer work with Ubuntu 17.10 Unity. Here is my workaround:
sudo aptitude install compizconfig-settings-manager
Goto "Commands" under "General". Under the "Commands" tab add
/usr/bin/gnome-screenshot in one of the (empty) lines. Goto next tab "Keybindings". Press the "Disabled" button on the line corresponding to the line where you added
/usr/bin/gnome-screenshot. Press "Grab key combination" in the popup window and press Print. Press Ok to close the popup window. The button on the line in the
ccsmwindow should now show as Print. You can now close the
Test with Print. The familiar "Screenshot" window with filename selection should now appear.
Multiple other keybindings can be added, e.g., one to
gnome-screenshot -a for an area-selected screenshot.