Since 2006 I’ve been buying a Logitech Trackman Marble (or, as Amazon calls it, a USB Marble Mouse) for both my home and work setups (they don’t die, I just seem to lose them somehow). It’s got a solid feel to it, helps me avoid RSI twinges and when I’m thinking I can take the ball out and play with it. It has 4 buttons, but I find the small one on the right inconvenient to use so I treat it as a 3 button device (the lack of scroll wheel functionality doesn’t generally annoy me). Problem is the small left most button defaults to “Back”, rather than “Middle button”. You can fix this with xinput:

xinput set-button-map "Logitech USB Trackball" 1 8 3 4 5 6 7 2 9

but remembering to do that every boot is annoying. I could put it in a script, but a better approach is to drop the following in /usr/share/X11/xorg.conf.d/50-marblemouse.conf (the fact it’s in /usr/share instead of /etc or ~ is what meant it took me so long to figure out how I’d done it on my laptop for my new machine):

Section "InputClass"
    Identifier      "Marble Mouse"
    MatchProduct    "Logitech USB Trackball"
    MatchIsPointer  "on"
    MatchDevicePath "/dev/input/event*"
    Driver          "evdev"
    Option          "SendCoreEvents" "true"

    #  Physical buttons come from the mouse as:
    #     Big:   1 3
    #     Small: 8 9
    # This makes left small button (8) into the middle, and puts
    #  scrolling on the right small button (9).
    Option "Buttons"            "9"
    Option "ButtonMapping"      "1 8 3 4 5 6 7 2 9"
    Option "EmulateWheel"       "true"
    Option "EmulateWheelButton" "9"


This post exists solely for the purpose of reminding future me how I did this on my Debian setup (given that it’s taken me way too long to figure out how I did it 2+ years ago) and apparently original credit goes to Ubuntu for their Logitech Marblemouse USB page.