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Exposing My Ignorance /
Figuring out the buttons on the Kensington Expert Trackball in Ubuntu

The short version:

In GNOME, the default meanings of the Kensington Expert Trackball's four buttons are:

  • Bottom-left: Left-click
  • Bottom-right: Right-click
  • Upper-right: Middle-click
  • Upper-left: Browser back

If, like me, you've used the Mouse control panel to switch things to left-handed mode, these are flipped left-right.


The long version:

I'm a trackball user. My workmates think I just do it to make it harder for them to use my computer. But the truth is, whenever I have to use a mouse for any length of time, my hand cramps up from the inevitable repetitive task of lifting the mouse up with my thumb and the side of my pinky to reposition it in the middle of the mousing area. I've been using a Logitech trackball happily for the past couple of years. Logitech only makes two models of trackball -- mine's the one that only fits your right hand. After an inspection by a workplace ergonomics consultant, I was advised to switch to mousing with my left hand to alleviate some issues in my right shoulder. So, I've switched to the venerable "Kensington Expert Trackball", an ambidextrous trackball with four buttons.

The tricky part is, what do those buttons do? Kensington offers configuration software, but for Windows only. A little bit of experimentation found that the bottom two buttons were the "right-click" and "left-click" buttons, but the other two were a little more enigmatic.

The first really helpful page I found on this subject, was one about mapping mouse buttons in Fedora. It advised me to use a program called xev to find out what Gnome button each button was mapped to. Clicking the upper-left and upper-right buttons in xev gave me (among other things) this output:

ButtonPress event, serial 33, synthetic NO, window 0x6400001,
    root 0x25d, subw 0x6400002, time 934193039, (51,37), root:(1978,83),
    state 0x0, button 2, same_screen YES

ButtonPress event, serial 33, synthetic NO, window 0x6400001,
    root 0x25d, subw 0x6400002, time 934193751, (51,37), root:(1978,83),
    state 0x0, button 8, same_screen YES

(I also later found out from here that I could have achieved the same thing by using xinput.) So now I knew the buttons were interpreted as "button 2" and "button 8". But what do those do?

From another post about the Logitech Marble Mouse (Logitech's ambidextrous mouse, which I was considering as an alternative to the Kensington), I found that Button 2 is equivalent to the middle button on a 3-button mouse, and Button 8 is "browser back".

Which left me with just one more unanswered question: What the heck does the middle button a 3-button mouse do, in Ubuntu? I found the answer here. The short version: A lot of stuff! Probably the most useful and easy to remember, are that it opens links in a new browser tab, and it copy-and-pastes highlighted text.

Probably the next thing most technical users would be interested in is, how do I change what these buttons do? Well, there's plenty of information about that on the web. A couple of good places to start:

In my case, the only modification I needed to make was to swap the buttons for left-handed use. And fortunately in Ubuntu, you can do that with the "Mouse" control panel!