Can anyone advise of a way to set a universal quit-application shortcut?

Solution 1:

Gracefully close a window

The simplest would be to add the following command to a shortcut key of your choice:

wmctrl -c :ACTIVE:

wmctrl is not installed by default:

sudo apt-get install wmctrl

from man wmctrl:

-c <WIN>
    Close the window <WIN> gracefully

Gracefully closing a window means that if you e.g. made changes to the currently opened file, you will be asked if you want to save the changes etc. This is similar to the Cmnd + Qyou are used to.

To add it to a shortcut key

Choose: System Settings > "Keyboard" > "Shortcuts" > "Custom Shortcuts". Click the "+" and add the command:

wmctrl -c :ACTIVE:

Or, if you are comfortable with Alt + F4

Even much simpler, as mentioned by @Takkat (thanks!), you can simply press Alt + F4

Solution 2:

using CTRL Q works to quit an application in Ubuntu 14.04